Dude -
I went through the same thing when I upgraded to the mogul for me and hubby. They gave me grief because my handset had only been on my line for less than a month when I changed to the mogul. I talked and talked to different people, even at retentions, they all told me they couldn't do anything, I needed to call the rebate people. Did that a couple of times, really a pain in the tookus.
In any case, I was hunting on sprint's site one day, while on hold with them, and found the rebate center, and filled out the contact info and sent them a concise email about my issues. Within 48 hours, I got a call saying that it had been taken care of. I checked and checked with them, but two weeks later I got my check.
You could try retentions, I wouldn't hold my breath talking to them though. They will tell you to call the rebate people.
Make sure you have all your info together before you send off the email. When you bought it, how often you sent the info, how irritated you are, how long you've been with them. ANYONE's name that you have/remember, put those in too.
Good Luck!
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https://www.sprintrebates.com/track/sprintpcs/email_us.html