Write to them and insist it is done..in the nicest possible way. If they don't the Gas people will probably come and check it. But we had a similar problem in that our boiler was not fitted by Corgi so had no safety certificate, and it seemed no matter who we phoned they couldn't care less even though they all said it was illegal.
In the end we called the Gas people and as the boiler was incorrectly fitted it had to be shut off and he had to do something or we by law could have got it done and he would have been billed.

To be honest it sounds like you need to think about moving.