I would try to weed out what sort of equipment you're on and what kind of connectivity your CO has. It's not the easiest thing to do in the world but I was able to determine after some piecing together why my Frontier connection is limited to 3M/384k. While I am out of a remote, it was discovered the DSLAM I come out of is a full blown unit you'd find in a CO and while old, had the capacity to handle higher speeds including support for ADSL2+ line cards (which even surprised me). It also has Fiber running to it but I was not given information on how fast that fiber is running at. My guess is OC3. I've also found out the remote I feed out of has new ADSL2+ and VDSL2 equipment (bonded DSL) ready to be turned up that is also connected to Fiber. But yet, no higher than 3Mbps, even out of the CO itself. Businesses can get 6Mbps without a problem though!
I recently got Verizon to fess up and give the reason why I was also limited to 3Mbps on the remote terminal I come out of (Litespan). I wound up getting a 5M circuit out of it on a remote capped at 3 and it's been like that for 5 months as a part of a test. Runs smooth and never drops even with my line running marginal (SNR of 7dB downstream, 9dB upstream ).
Either way, find out some technical info or keep pestering
Oh yeah, peak hours for my neighborhood on Verizon:
Also a video of how well it performs which took just a few minutes to upload (there's some delay for the first site, buffering issue on Verizon's edge router I'm getting them to fix):