It's most likely a compromised situation you're not aware of on your end. Please follow all the steps and reach out to CSA (also in the post).
I am an Official Comcast Employee on the Identity Product Team and the Serviceability team at HQ. Official Employees are from multiple teams within Comcast: CARE, Product, Leadership. We ask that you post publicly so people with similar questions may benefit from the conversation. Was your question answered? Mark the post as Best Answer!