I can subrent, but need pass rental company's credit check.

Thanks. My contractor is I can sub rent but have to pass the rental company's credit check. Since the mother move in, I don't want they stay, so I did not going forward to do their credit check. Yesterday, they sent me letter said they will sue me for "double damage". They said we have written agreement in their room. It is not true. Later they may say that it is me take their rental agreement. The letter is someone knows the law helped. I can't even sleep now.