Assume you have tried everything and got to this stage
Guide: How can I sort out my network issues?
Guide: Is the network down for me or everyone?
As to your options the terms and conditions are clear that you are not guaranteed signal everywhere.
Paying what's left of your contract is probably it.
You could argue your corner if this is very long term, but I wouldn't hold out hope.
The one option you haven't got is stopping your Direct Debit, a couple of missed payment and things are handed over to debt recovery and bang goes any chance of getting a contract elsewhere
This is not O2 and we are all customers here similar to yourself and cannot answer account type queries.
