irritatedbeyondbelief I would agree it sounds pretty messed up. First off this is a user supported forum and not even the handful of TMO employees that help and moderate this forum have account access.
I know usually the process for paying off your previous carrier and sometimes is not explained as clear as it should be by some reps is that they don't pay off the other carrier, they reimburse you for paying off the other carrier. Typically the process is that you submit your final bill to T-Mobile online, you ship your phones back to T-Mobile and then once it is approved they send you a pre-paid debit card with that amount as a reimbursement for your expense of leaving your previous carrier. From some of what you described, i.e. "sending the phone back to other carrier" T-Mobile doesn't do that they just pay off the balance and send the phone to a company that refurbishes them and sells them or uses them as insurance replacements. Sending it back to the other carrier would require cooperation between the carriers and the other carriers especially AT&T & Verizon really don't like T-Mobile because of the disruption of the cell market and have forced them to give up their 50+% profit margins they were making off their customers.
Just as a note also that not all T-Mobile stores are "corporate" stores some are authorized resellers which IMHO are a little less informative but again that is just my opinion. Hopefully you have some documentation showing you turned the phones into the store?? I know when I do a JUMP (upgrade) at the store they always give me a reciept for the device I have given them.
I am not sure what avenues you have been using to contact T-Mobile but would highly recommend if you haven't already contact T-Force on Facebook or Twitter. They have an awesome reputation for resolving complicated issues especially ones with missing credits and etc. Here is a link;