Received letter from Xfinity stating someone changed preferred email address

As stated, I received a letter stating "you or another user recently changed one or more of the following features" "your preferred email address was changed." When I signed in the email address seemed to be unchanged. However we have been victims of identity theft recently with fraudsters attempting to steal some of our other accounts. Clearly we do not want to post our account information in a public forum, how can we directly contact someone? I'd write an actual letter, but your letter contained no return address (even on the envelope!).