I managed to get this resolved by kicking up a fuss. Honestly it wasn't easy
I got through to CST and had this issue raised. Nothing was happening for weeks so I wrote into sky saying I would basically have to take further action and that it needed escalating.
I finally got this referred to networking with a promise of call-backs. These never occurred.
Networking kept making small changes e.g. capping my line etc claiming it would help. I had to keep getting the case bounced back to them as they kept closing it by just changing my sync. This must have happened upwards of 5 times.
I then posted over on here
http://helpforum.sky.com and eventually got through to somebody who tweeted sky on my behalf. I then got in touch via email on this forum with a sky forum helper who said they would investigate for me
I also wrote a recorded letter.
Nothing for several more days but finally things went back to normal. I had no official response but I can only assume that somebody did something. My line problems began to show in January.
All in all you need a lot of patience. Is it worth it, possibly not. Sky need to get a dedicated team onto this particular issue and stop messing us about. I would have adopted the sky fibre product but the way I'm feeling is to ride this 12 months out and switch to bt infinity.
Hopefully everyone gets back to normal soon!