missing phone shipped to tmoble

Has anyone else had an issue with swapping out a phone on warranty then shipping the old one back to tmobile to be told MONTHS later that they did not receive the phone and charging over $1000 fee on a paid off phone that was broken???? tmobile is being no help at all. everyone I have contacted basically says so sorry, too bad for you! they finally "supposedly" opened an investigation through their warehouse but I've yet to receive email confirmation of that. I REALLy do not want to pay $1000 for a paid off broken phone that I mailed back!! I saved the shipping receipt for over a month but had no idea there would be an issue. Is there no way to track the actual phone?????