I had to call TalkTalk yesterday, turns out they now have a call centre in the Philippines, what a difference. Knew what he was talking about and was totally coherent, nice work TalkTalk.
Nope, not resolved yet. I spent the best part of 2 hours on the phone Thursday night to Mumbai dicking around with umpteen different settings until FINALLY he accepted that the fault must be with the modem. They're sending me a new one.