Assurant return concern

I made a claim on my device at the end of January. They sent me the replacement device really quickly. My husband took my damaged device to a drop-box at USPS within a week of receiving the new device. We kept getting letters in the mail throughout Feb. that they still had not received the device. I kept checking with my husband to make sure that he had dropped it off like he had said and he kept telling me he was 100% he put it in the box himself. He remembers which car he was driving, which post office he went to etc. Come last month, April, my phone bill is $500 higher after being charged an unreturned device fee. We filed a missing mail request with the post office that a month later has still not turned anything up. The tracking number that Assurant gave to me says that it was never even scanned at the post office so it looks like they never received it. My husband put it in a drop-box so he never got a receipt or anything for it. We don't have the device and have done pretty much everything we can on our end to find it and no luck. I asked the Assurant rep the last time we were on the phone if they were going to make us pay for a device we no longer had possession of because the post office had lost it before it could be scanned and they just said yes. There is no way that there have been this many cases of almost the same exact thing happening and it's just a coincidence. There's got to be something more going on. I also am refusing to pay for a phone that I don't have that got returned and was lost once it was out of my hands. This sounds like a scam. 

T-Mobile, however, has been very helpful. They have put the unreturned device charge on hold and have let us pay our normal bill while we're trying to figure this out. They even waived our late payment fee since we didn't pay our bill due to the device fee.

Assurant will definitely be losing my business after this fiasco.