Your down SNR of 10 db is pretty high, the standard profile is normally 6db, though if your attenuation is 64.5 even with your internal wiring as it should be, then you must have a very long line or a line with a fault somewhere, so 10db may be ncessery to keep things stable!
Do you have a router supported by DMT tool (German page i'm afraid but just search for your make and model and see if it comes up:
http://dmt.mhilfe.de/), if so you can potentially tweak your down SNR that your router tries to sync at, so if you;re at 10db, reduce it by about 70% and try and make it sync at 3db.
For me, 3db is perfectly stable, but then my attenuation is 43db.
If you can find a better SNR you're still stable at (try pingtest.net etc, make sure you aren't loosing packets) then perhaps Virgin will lower it for you.
For the record, you can do all this with BE yourself using their website.