Tenant Refuses to Leave after house is sold

We have sold a house, closing on 8/30. The people in it have known it was for sale since March. They are refusing to leave. They are not answering any form of communication, we have resorted to certified letters to even ensure that they get any communication at all. They won't answer the door, the lawyer, or the real estate agent. She also is not paying the rent any more. CT law does not allow evictions until 8/25. The buyers are not sure if they are even moving in or want to go through with it because she was supposed to be out on 8/1. What do we do? Soooo frustrating.