Sorry I can't offer much advice, but have you contacted
Citizens Advice? They have a lot of advice about various situations on their site, and if you can get to your local branch, they will try and help you, including offering legal advice.
And the service is free.
I personally can vouch for them as they helped me sort out another problem a couple of years back.
I had a problem with Npower threatening legal action because I had apparently continually either refused their meter readers access to my property , or been out when they called, when I had actually been in on every occasion they said they called and no one had turned up.