Sounds about right, they are a bunch of c****. We moved and had a right to-do with them.
Long story as short a I can.
Signed up for the 'free' evening and weekend calls package a few months before moving house. Didn't realise but this had an 18 month contract in the background and if you leave BT they charge you the rest of the 18 months line rental. In our case about £112.
So we had to stay with them when moving to new house.
New house. According to them there was no phone line and they were going to charge us £122.50 to connect. There was a phone line but it had been unbundled to Virgin.
So we had the choice of leaving BT for £112 or staying for £122. In the end they waived the £122 if we agreed to sign up to another 18 month contract.
Getting the BT broadband is a whole other issue which went badly wrong but that's another story and I'm sick of hearing myself complain about it so won't.
So to answer your question, look at the contract length you signed up for, you probably have a few months left and under the agreement you will have to pay the remainder of the cost.
My advice would be to give them the money, tell them to go f*** themselves and run like to wind to another provider. Me bitter never!