I've had pretty good luck with the forums on DSLREPORTS.com. The ISPs usually have a tech or two that monitors the forums and is empowered to help.
About 6 years ago, I was using PacBell (now AT&T) and was losing DSL connectivity for 3 minutes every night at 11:44pm. Deep down, I knew that some sort of automated line test was going on, but I couldn't get any of the techs on the tech support line to do anything. I complained on the PacBell dslreports forum, and a tech took it as a personal challenge to discover the problem. He had people monitoring things through 3 nights of 3 minute outages, and then the problem went away. They never copped to anything. I was prepared to make a stink as a member of the tech press, but I was happy I never had to resort to it.
These days, I use a small ISP where the tech support number is a "hello line." If I have a problem (and its only happened twice in 4 years), I call the number and a tech says "Hello?" No nonsense. They are Sonic.net, and if they service your area, I strongly recommend them.
Anyway, to answer your original question, check out the forums on dslreports.com and see if there's a tech you can get interested in helping you.
-Llama