Hi Trish,
I am experiencing exactly the same problem as you. 4 months ago I moved from BT to TalkTalk. This monday I contacted them to explain that I was moving — I was utterly astonished to be told by TalkTalk that I needed to phone BT and take up a contract with them to be able to continue receiving the TalkTalk service. Then I could cancel the BT contract after three months, or buy myself out of it!! That is simply unacceptable.
Do please let me know the outcome of your dealings with OFCOM and TalkTalk so I can do likewise— a coordinated barrage of customer complaints may carry some weight . . . yeah right.

BTW I found your post by googling [talk talk" "moving home"], your post is the first returned result.