are phone sex lines illegal to use Watch
I am really surprised that your network did that to you. I would guess that it is more to do with the problems they run into with the huge £/minute cost of those premium services than with them trying to pass moral judgement on you.
If you aren't on a contract I would just tell them to stick it and go to one of their competitors. Get a new sim with a new provider and call the new provider's customer care line to have your old number ported over to the new sim.
If you are on a contract then you need to call your current service provider and ask them what's going on. If they try to force you to pay out the remainder of the contract you should inform them that you feel that you are being treated unfairly and that you will be having them investigated by the Telecommunications Industry Ombudsman if they proceed with that demand. You can do a google search for the contact details and website of that Ombudsman - it is their job to make sure that all companies within that industry operate fairly and do not exploit customers. Telecom Industry Ombudsman investigations are expensive and all costs are covered by the company who is being investigated (even if they are not found to be in the wrong!). For this reason, most Telecom companies find it cheaper and easier to settle the dispute amicably when you make the threat of involving the TIO.