I have bats in my chimney that I cant start a fire in to get rid of. How do I get rid of them?

The chimney is closed off and we cant axes it because the wall has been closed over it. We just noticed that we have bats going in and out, they can get in our walls and maybe into the house. Our house is two hundred years old and we don't want to let them destroy our house. I know of a house with bats in the attic, they have been there for 50 years or more and the house really smells bad. PLEASE HELP.