Fraud--Payment posted to my account from false bank account (when I paid by debit card)

I made a payment by phone in July with a debit card.  Didn't notice on my emailed receipt that it said it came from a bank account ending in 4 digits that no one in my house has.  Now a month later I received an email saying the payment was returned.  The debit card charge is still on my account and the phone number attached to it was a third party bill paying service that says they take the Xfinity payments.  I tried doing the xfinity chat support for over an hour and got no where--the customer service rep didn't seem to believe me.  So I need to figure out how to get my money I paid applied to my account since this was obviously fraud.  I mean do I report it to law enforcement?  Some kind of business bureau?  Hopefully this reaches someone that can help