you'd be better off calling retentions now, while your still in or close to the cooling off period and start as you will find you need to go on, by threatening to leave
They are traffic shaping by usage type, so a 20 minute download at the speed yourpaying for is now taking 4 or 5 times as long and making it seem like you are a heavy downloader when you may not be
I ran a speed test on mine the other night via one of those test sites, it reported no faster than 20meg download
... although to be fair the laptop i used may not have been configured 100% correctly, and i didn't fire up any downloads, but i am not happy, because it means the home plugs are NOT the restriction in my current setup, but i have no real way to prove it without installing a system where i normally have one but don't right now
EDIT:
Just as an after thought, ecksmen, i know you said you were getting full speed and now it has changed, i would be tempted to run a tcp/ip optimiser on your pc, just in case an update or something screwed with your settings