I had this a loooong, looong time ago back when I was with NTL (VM) and in my first Uni house. I couldn't play games at all, instant 500-1000 ping.
The only times I could get an online game going was from about 23:30/00:00 to about 10:00 then the problem came back. Does it affect you 24/7? I complained a few times but they always denied a problem.
Sorry to say but it just automatically fixed itself...2/3 months later. I eventually put it down to a traffic management/dodgy exchange issue and moved on with my life. Huge pain in the backside though.
Call them up and ask wtf!