Chief Financial Officer at Charter Communications
Thanks, Chris. Now, let's turn to our results on Slide 5. We will continue to reference the COVID schedules we provided last year and included again on Slide 17 and 18 of today's presentation to help with year-over-year financial comparisons. We grew total residential and SMB customer relationships by 185,000 in the third quarter and by 1 million in the last 12 months. Including residential and SMB, we grew our Internet customers by 265,000 in the quarter and by 1.3 million or 4.4% over the last 12 months. Video declined by 121,000 in the third quarter, wireline voice declined by 216,000 and we added 244,000 mobile lines in the quarter. As of the end of the quarter, we had 3.2 million mobile lines. Despite the lower number of selling opportunities from cable sales, we continue to drive mobile growth with our high-quality, attractively priced service rather than using device subsidies.
Moving to our financial results starting on Slide 6. Over the last year, we grew total residential customers by over 900,000 or 3.2%. Residential revenue per customer relationship increased by 5.6% year-over-year, given last year's third quarter, residential revenue adjustment of $218 million for sports network credits that we provided to video customers, as well as promotional rate step-ups. Video rate adjustments that pass through programmer rate increases and a greater mix of longer-tenured customers. Those were partially offset by the same bundle and mix trends we have seen over the past year, including a higher mix of non-video customers and a higher mix of choice, essentials and stream customers within our video base. Keep in mind, that our residential ARPU does not reflect any mobile revenue. As Slide 6 shows, residential revenue grew by 9.4% year-over-year, reflecting customer relationship growth in last year's COVID impacts.
Turning to commercial, SMB revenue grew by 7.5%. This growth rate reflects COVID-related impacts of $11 million that negatively impacted the third quarter of 2020. Excluding this impact from last year, SMB revenue grew by 6.3% faster than the second quarter growth when making the same COVID-related adjustments. Enterprise revenue was up 6.4% year-over-year, and included some one-time fees which were a benefit in this quarter. Excluding the benefit from this year, enterprise revenue grew by 3.8% and by 6.5% when additionally excluding all wholesale revenue. Enterprise PSUs grew by 4.5% year-over-year.
Third quarter advertising revenue declined 15.1% year-over-year, primarily due to less political revenue in 2021, partially offset by COVID impacts last year. When compared to the third quarter of 2019, advertising revenue declined by 0.8%, primarily due to local ad revenue, particularly auto, mostly offset by our growing advanced advertising capabilities. Excluding auto, the third quarter advertising grew by 8% over the third quarter of 2019. Mobile revenue totaled $535 million with $201 million of that revenue being device revenue and other revenue grew by 6.5% year-over-year. In total, consolidated third quarter revenue was up 9.2% year-over-year.
Moving to operating expenses on Slide 7. In Q3, total operating expenses grew by $460 million or 6.2% year-over-year. Similar to revenue, the year-over-year operating expense growth rate is elevated due to 2020 COVID effects, programming increased 9.4% year-over-year due to last year's third quarter benefit of $163 million related to sports network rebates and higher programming rates. These factors were partially offset by a higher mix of lighter video packages such as choice, essentials and stream. Regulatory, connectivity and produced content grew by 3.5%, primarily driven by higher regulatory and franchise fees and video CPE sold to customers.
Cost to service customers were essentially flat year-over-year compared to 3.3% customer relationship growth. Excluding bad debt, cost to service customers declined by 2.8% year-over-year and that's despite a higher number of customers and outsized hourly wage increases that we put through earlier this year. Bad debt was higher by $47 million year-over-year, but still nearly $75 million lower when compared to the third quarter of 2019.
Marketing expenses were also flat year-over-year, primarily driven by the lower sales environment. Mobile expenses totaled $607 million and were comprised of mobile device costs tied to device revenue, customer acquisition and service and operating costs. And other expenses grew by 3.8%, driven primarily by higher corporate costs, partially offset by lower advertising sales expense year-over-year given the absence of political revenue this year. Adjusted EBITDA grew by 13.9% in the quarter.
Turning to net income on Slide 8, we generated $1.2 billion of net income attributable to Charter shareholders in the third quarter versus $814 million last year. The year-over-year increase was driven by higher adjusted EBITDA.
Turning to Slide 9, capital expenditures totaled $1.9 billion in the third quarter, below last year's third quarter spend of $2 billion, driven by lower scalable infrastructure spend, primarily due to a stabilized level of network traffic growth and investments made earlier this year, a decrease in line extension spend driven by housing build delays due to supply chain constraints in the housing industry and lower support capital primarily due to timing. We spent a $119 million on mobile-related capex this quarter, which is mostly accounted for in support capital and was driven by investments in back office systems and mobiles to our build-out. For the full-year 2021, we expect cable capital expenditures to be relatively consistent as a percentage of cable revenue versus 2020.
As Slide 10 shows, we generated nearly $2.5 billion of consolidated free cash flow this quarter, an increase of $722 million or 41.2% year-over-year. We finished the quarter with $87.9 billion in debt principal. Our current run rate annualized cash interest, pro forma for financing activity completed in October is $4.1 billion. As of the end of the third quarter, our net debt to last 12-month adjusted EBITDA was 4.32 times. We intend to stay at or just below the high end of our 4 times to 4.5 times leverage range. During the quarter, we repurchased 5.3 million Charter shares and Charter Holdings common units, totaling about $4 billion at an average price of $753 per share. Year-to-date, we purchased $12 billion of our stock and common units and since September of 2016, we have repurchased $51.4 billion or 37.5% of Charter's equity at an average price of $436 per share.
Our results show that even in this unusual environment, our flexible and robust business and service model which benefits economically from lower customer transaction activity still drive outstanding EBITDA and free cash flow. Coupling that with our unique balance sheet structure and a proven capital allocation strategy, we will continue to produce shareholder value for years to come.
Operator, we're now ready for Q&A.