Ignorance is no form of defence.
As T&Cs seem to be made more beneficial for the customer nowadays the companies have to make some money when customers change their contract.
Unless I'm wrong, a supplier is supplying a service at a particular address and they are under no obligation to supply at a different address with the same contract. Granted if you have been on a monthly contract then that should be offered at the new address.
If you look throughout these forums then you will see that major changes seem to form a new contract. Eg new router, upgrade to faster speed (VM), etc.
Was Eclipse Home Option 1, VM 2Mb & O2 Standard
Now Utility Warehouse (up to 16mbps) via Talk Talk