Just a couple points:
1) Was the upgrade performed at an official T-mobile store or an authorized reseller? In either case, it's difficult to put the blame on one sole person. Is it the rep's fault? Possibly, but how would the CSR know that he was dealing with a scam artist rather than Mr. JMillion? I am saying this because it is difficult to blame T-mobile for this. Since the check bounced, did you request a copy of the check to see what the name and address is?
2) You can get the best deals by talking to Loyalty. Call T-mobile and after entering your number and last 4 of SSN, say "cancel". Here are some deals I have gotten recently. HTC One S and Galaxy S2 free of charge, waived upgrade fee, free shipping. And Galaxy S3 for $180, waived upgrade fee, waived shipping.