charge an early termination fee for equipment returned on death of my mother

My 92 year old mother was talked into switching to an Xfinity security system from ADT under the promise that she would not be charged any extra fees if she died before the two years.  Unfortunately, I’ve been fighting with Xfinity for 3 1/2 months trying to get a $275 fee charged on the last bill for equipment. We returned all the equipment and have a receipt for that. I’ve called repeatedly and get different answers each time.  At first I was told that the charge was for unreturned equipment. But then, when I informed them, we had indeed returned all the equipment, and I was told it was an early termination fee. Then I was told Xfinity would waive the fee when someone dies but I needed to upload her death certificate, and fill out some forms, which I did. I’ve been calling now for 3 1/2 months probably close to a dozen times. The last woman I spoke to today -a woman named “Lerato” -was obnoxious and argumentative and now claims no refund is due.  I can’t believe this company would hire people like this to argue with a deceased’s relative who has been spending hours trying to get money back from a company who would intentionally mislead an elderly woman.  I plan to file a small claims action on principal if this does not get resolved.