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

This same thing has happened to my family. We sent the phone with the pre posted envelope they provided and then now I finally hear that they never got it. This makes me so upset they are trying to charge me the whole price of my device that I returned just the exact same way I have always sent it and never had a problem. This is a huge problem! Not cool at all that this is happening to so many people! Not cool at all! I can't believe this to say the least...we have been with tmobile since before they were tmobile and never ever had a problem like this. I really hope they can find it because this is such a head ache and so un fair can't believe this. If this isn't fixed by them my family and our 8 lines will for sure switch up company's for a company who will be more responsible for their mistakes. My next step will be small claims court tho I really don't want to but I also feel that they need to be held responsible. Saving all of these same complaints in my records as well. Might help in the future especially if this goes to court.