I had this issue happen with my AT&T DSL line. I even got to the point where a technician was supposed to come out and look at the line but he never showed up.

I had this issue happen with my AT&T DSL line. I even got to the point where a technician was supposed to come out and look at the line but he never showed up. I called back, I jumped through all their hoops, and then they eventually connected me to another more advanced department who just looked a few things up, said "ok, here's the problem, hold on gonna put this order through to fix it." Within 2 minutes my connection was back to 6Mbit. Whatever they did they were able to do it COMPLETELY REMOTELY. I never found out what was going on but I suspect I may have ended up on some sort of black list, maybe because of torrents or some other traffic profiling. It blew my mind. I suffered that speed for nearly 3 months before getting it fixed.