Continue billing for deceased account holder

Hello.  My mother passed away in late November and I have sent Xfinity her death certificate several times, along with the form from the bereavement support part of the website.  Her Xfiniy cable was canceled with no issue, but I have wasted hours of my life on the phone with customer service representatives who do not give me accurate information, cannot access all of the notes on her account, and pawn me off on the store.  I have gone to the store twice and they get very annoyed at the call center for sending me there and made notes in her account for me, which didn’t end up helping.  Her account is closed but they are continuing to bill for the month after she died as well as for the device, which I have been asking how to return since day one.  They said they emailed me a label, but that was not true.  No one knows what they are talking about and I am BEYOND frustrated.  I will never do business with Xfinity in any capacity after this horrible experience.  Can you help me in any way?  Please…