Being charged for phone after returning back to Assurant...

I have had similar issues. Been a T-Mobile customer for 15 years and I will be leaving to another carrier after this experience. Received a new phone from them and mailed the old one back with the supplied return label. 3 months later I get a charge on my T-Mobile bill for a non-returned insurance claim phone. I tried contacting Assurant about this and after being on hold 30min, finally got through. They asked several questions to verify my account and identity and when they got to my billing address they said it was wrong. I told them they are wrong. They told me to look at my online account to verify. I did and they still said I was wrong. I then proceeded to attempt sending them a PDF of my bill to verify themselves and they said they can't receive any files; which is a lie, because I sent all my original return documents digitally. I then asked to speak with a supervisor and was told that they were busy and would call me back on Monday. It's been over a week and still no call back. This company is nothing but a scam. I went on reddit and found countless other people who have had the exact same issue with this company.