T-Mobile changed migration fee amount after call to switch plans Internet

Back in February I decided that T-mobile's monthly 4G plan was a much better deal than the 60 dollar a month package I had been paying for (and hardly using any of the minutes they charged me for).  I had been on contract with them since July of 2011 and had decided to make the switch when the plan showed up in the plans section on the site with a 120$ migration fee to make the switch.  I waiting a month to get the money ready for the switch and for my next bill.  When i went to make the switch it was no longer available online and said that the only way to activate it was by phone.  I called and spoke with a representative and we agreed to make the switch to Monthly 4G and that I would be charged a $120 migration fee + a bill for the prorated month.  I agreed to this.

A few months later, and not a single bill was received from T-mobile.  The online payment center showed a balance of 0 (and still does) and there was no way to pay the fee.  I honestly figured they had somehow forgot about me... NOPE!  Just last week I recieve a letter in the mail saying I am behind on my bill and will be sent to collections for $243!?  This number is pulled out of nowhere, and is the max amount t-mobile charges for an early termination fee, and not the amount that was agreed on.

I called their customer care and they were solid on me paying $243.  The lady I spoke with would not change her stance and I finally asked to speak with her supervisor.  Her supervisor was impossible to understand on the phone and only repeated the same garbage to me saying they hold the right to charge an early termination fee up to $200.  I was lied to and cheated.  I argued with them for almost an hour until my phone ran out of minutes dealing with them.  At this point I have no clue what to do with them, and say let them send it to collections, and when they do, I'll tell them I agreed on 120$ and that's what I will pay.