Lied to and billed for a phone that I was offered for free

I wanted to come back and update my reply since I was able to get this situation resolved.  The morning after I typed my experience above, I got an automated text message survey asking about my experience.  I was very honest in the survey, giving low ratings and a full explanation as to what went on.  Later that morning, I missed a 1-800 call but didn't answer because I was out with a friend.  I received another call from that number an hour later, but again did not answer since I was still out.  When I got home and listened to the VM, I learned it was T-Mobile calling to discuss my survey and wanting to help resolve my issues.  Unfortunately, the number they left for me to call back was just the general customer service number, so I opted to wait and to a T-Mobile store instead.

 I went to my local T-Mobile store (they are an "authorized retailer" as opposed to a corporate store, and as I expected, they were unable to provide any assistance.  Despite the T-Mobile rep on the phone telling me I could return the phone to the store, the store associate said they could not accept the return and that the only thing I could really do is call in to customer service again.

I had planned to visit a corporate store the next day but decided to call customer support one more time since it was too late to go to the store that evening.  I called customer service, explained that I was returning their call about my survey.  The rep asked for a rundown of what was going on.  She checked the notes on my account, and just like the original poster above, she found no notes confirming that the rep told me the phone would be free after the promotion was applied.  The rep then explained that while they do have other phones that would be free, the once I received would be $99.  She then put me on hold to speak with her supervisor and see what else could be done.  A few minutes later she came back on the line and said that rather than put me through the hassle of exchanging the phone, she was going to apply a credit to my account.  She said it would have to be a lump sum and it would just go towards my current bill (as it couldn't be applied to the monthly fees for the phone), but that was totally fine with me.  That's all I wanted from the start.  

So all in all, it was a whole lot more complicated than it should’ve been and took way more time than it should have, but T-Mobile did resolve the issue and stand behind what I was originally promised by one of their reps.