willodan
I'm sure that before they will consider anything regarding the Early Termination Fee when cancelling, they will need to do some troubleshooting. To begin that process, you should start a new topic in the Tech Support section, which you can do here. There could be a number of things causing the issue, and troubleshooting will help to pinpoint what they are, or what it is, if it's a single thing. I know that you've already done troubleshooting and they've sent techs, but the reps here will probably still need troubleshooting to be done. I could be wrong, though.
The only other thing I can suggest here, if you haven't already tried it, or they haven't suggested it, is turning off, or snoozing, the Video Data Saver while you're viewing the Youtube videos or streaming.