T mobile offer not honored

After looking at what AT&T offered (30 months for the same rate) I agreed the letter was probably a mistake. OK fine 27.67 for 30 months (full retail for the phone). But THEN the rep said since my phone numbers were coming from a business account, they could only sign me up for a Tmobile business plan for 90 days. Anybody ever hear of this?? The business plan cost twice as much as the 55 essentials plan I wanted. The rep said I shouldnt worry because HE PERSONALLY would credit my phone bill for the next 3 billing cycles and then I could switch over to the consumer essentials 55 plan. They would give me nothing in writing about this credit until I insisted the rep write a letter on their letterhead detailing I was entitled to this credit for 90 days. Doesnt mean much but at least I got something in writing. The next day I call Tmobile and it took about 20 minutes for the customer service rep (a very nice person) to switch me over from my business plan to the Essentials 55 plan. All I had to do was pass a credit check and agree to be personally financially responsible for the account. Thats it. I now wonder if the letter was a mistake and I feel like the store was just trying to get another couple hundred dollars out of me with this " you have to have a business plan for 90 days before you can switch to a consumer plan". Anybody ever have to buy a more expensive plan in order to get the cheaper phone plan later on?? I feel like I was taken advantage of.