Fraudulent bill activity on a senior citizen: How can we get a human being?

My 81 year old mother has an Xfinity Internet package/account.  She got a call last week from a fraudster purporting to be from Xfinity  promising steep Xfinity discounts, etc.  She's aware of this kind of stuff, recognized it as fraud, hung up, and reported it to Xfinity.  At that time, after a long wait, she was able to speak with someone who confirmed that Xfinity does not do any deals like this and that it would be taken care of.

But, it appears the fraudster did some kind of bogus eCheck deposit into the account anyway.  It bounced.  Testing an account is a common tactic but totally out of her control.  Now, she has a $25 charge for an Echeck/EFT return fee on the latest bill for a deposit she never made in the first place.

She has been trying to get through to a human for several hours over a couple of days and is not able to get to anyone at the 1-800-934-6489 number.  The Chat service doesn't let her get to anyone either.

Looking for help and advice on whom to call to get this taken off her bill.  

Thanks.