We had an intermittent issue here some months ago, similar to your woes. It would perform erratically, working fine for a while, then dropping out for hours. I spoke to several support people working for the local Roadrunner, who tried to be helpful, but weren't. Eventually I got in touch with Warner Cable (now Charter) directly, told them I needed reliable 24/7 internet, and that if they couldn't provide it, I'd be forced to move to their competition (FiOs, through the phone company)--reluctantly, because I'd rather stay with Warner (the devil that I know). After that, it got fixed. I'm sure it was some hardware in the area--cracked cable or marginal amp or distribution hub kinda thing. Whatever it was, they fixed it. You don't have that option, going by your posts. That really sucks. Maybe you can find an alternative anyway, and bite the bullet on the expense until this all gets sorted. I know you can use a modern cell phone to create a hot spot, for example.
