keep getting threatening enails about equipment that was returned

Doesn’t matter, - T Mobile  printed the packing slip, Its the UPS Drop off locations fault they gave me no receipt.  I know where the modems go back to- so just for that I know more than your customer service person - They go back to Ft Worth!  You guys printed the packing slip for return, you pay UPS shipment costs for that- surely somebody should be able to pull a Record!  Where's the initiative?

You have no records? A billion dollar company, tries to screw people? Bottom line I am not paying for negligence either on your part nor the Drop off center for UPS here in Texas.

And since when does a Modem cost $450 either, I have used T-Mobile probably over 20 yrs if this does not get resolved, trust me , it will be known all over the place that you folks try to rip people off.

I have further evidence that I have dug up where other people did have a tracking number and you guys still tried to bill them.  I am asking that T-Mobile try to rectify this , not get into "Well we can't find it here is your bill" I have ZERO PROOF any effort has been made on your side, just mine to defend myself. T Mobile will  lose a long time customer over this if it does not get resolved. Plus many more will know.