Keep received text message for returning device

I canceled my plan and have already paid the final prorated bill. However, I am still receiving text messages from Xfinity asking me to return a device that I have never had.

I visited a store, and the agent confirmed that, according to the system records, there are no devices associated with my account that need to be returned.

I would appreciate your help in resolving this issue, as I do not want to continue receiving these messages.