Did you get anything in writing to secure this information? Did you get the names of the staff members that told you this offer ? Sounds a bit sketchy to me, if you have no proof of who you spoke to or nothing in writing (or even some pamphlet detailing these offers) then there is not alot you can do, other than call head office, with dates you were in there particular T-Mobile store....I have found myself in a similar situaion regarding a credit card, and the dispute went on for 6 months and I got nowhere, because I hadnt got the names of people I had spoken to which is easily done. Word of mouth isnt much to go on im afraid.