It looks as if you might have to continue paying the fixed charges at your old address until the end of your contact period. The following is taken from the TalkTalk website. (I've split it into two paragraphs as it's the second paragraph which is the relevant bit - although it wouldn't make any sense if I didn't post the first bit!):
"If you move house and want to access the Services at your new address you may need to set up new accounts for that location by calling Customer Services. You will have to provide us with what we regard as suitable proof of your new address if you wish to receive the LR Service or the Broadband Service. We will follow good industry practice in deciding what proofs of address are required.
If you do not provide this information we will not be able to terminate your existing account and you will be liable for any charges that remain due in respect of the remainder of the term for the particular Service (for example, the remainder of the Minimum Period for the Broadband Service)"
http://www.talktalk.c...lk-product-terms.html
Chris