Assurant return damaged device package Empty!!

I am dealing with the same issue right now, we put a claim on December 2022 we also got our devices,  but I feel like we been scammed,  we did return the broken devices but unfortunately assurant said they received an empty envelope, I did asked them to run an investigation on it because I know I was the one who send back the devices,  I took my time to tape the envelope also to walk in to the post office to make sure they weight and scan the envelope. It is so frustrating to do investigation on assurant and post office,  hoiii , they wanted me to pay $800 for the devices not received,  but I am so frustrating  knowing that I have proof they received the package,  it's a scam,  I do not know what to do now, every time I call they said sorry for the inconvenience but you have to pay , I said what? Can someone please help me with this situation 😫