I am having exactly the same problem, been over a week now.
The engineers been out my internet speed is fine he tried the box reset and that didn't work then he actually installed a new box and still nothing . The lastest from talk talk after about 4 calls,is that they are passing it over again to the help desk people , they ran tests on Saturday and said it was working . There now sayin I will get an update on Tuesday.
its a bit ridiculous now the guy that came out said he's never seen this before it's like theve been switched off.
talk talk are saying its sky's problem ?