A letter of defamation

I have been having problems with our Parish Council who has refused to deal with a rat infestation resulting in our property being damaged by vermin. They have now been issued with an Enforcement Order which they are taking very badly. They have accused me of making false accusations and have called me a vexatious complainant so are refusing to deal with me. I have evidence of everything I said. They have copied in all the people that I have turned to for help ( Their superiors) and in doing so have tried to influence their opinion of me by trying to destroy my charachter and my credability. What is the best way forward?