Had same problem for many years with Time Warner. They used to deny they were interfering, but in the last year or so, the new owners at least will admit they don't "support" VPNs.
Like clockwork, my VPN service would be cut off after 10 to 35 minutes by Time Warner - now owned by - Charter / Spectrum. I switched my VPN service to ExpressVPN and have had no problems since. A single account cover 3 devices, say two computers and your cell phone.
Here is my very amateur understanding of what is going on technically:
The cable providers are trying to stop gamers and folks trying to defeat Netflix geographic blackout areas using VPNs, and maybe privacy itself. (Personally, I am not a World of Warcraft player or Netflix tweaker.) At the same time, some of their major custormers must have access to VPN connections to protect brief and critical business and financial transactions. So the compromise is to allow the VPN connection to run for a long enough time to complete a few brief financial transactions, and then kill it. Some VPN service providers have developed systems that defeat the methods ISPs use to detect continuous VPN connections. Technically, from what I have been able to observe using PingPlotter, what they are doing is changing the routing paths every so often, far before the ISP's system detects a longer term VPN connection, thus defeating the ISP's detection and kill process.
If my understanding is wrong, please correct it. If anyone has a more accurate technical explanation of what the ISPs are doing, I would like to be better educated on this topic.
We all need to do whatever we can to fight back against these attacks on Network Neutrality, and taking the profit out of the effort by taking away access to our private information seems like the most direct approach.
In addition, the day the Verizon lobbist currently in charge of the FCC succeeds in gutting Network Neutrality, I have pledged to switch my cell phone services away from Verizon to Credo (warning - Credo is well known for poor customer service - but the personal bother is worth it in this case). I call Verizon customer service every so often and renew my pledge.