Complaint Review: T-Mobile

I purchased Samsung galaxy S6 Edge phone from T-Mobile at their retail office, T-MOBILE 9168, 2710 W University Dr Ste 1040 Denton Tx 76201-1606, dated 04/11/2015 at a total cost of $904.43. I payed for this device on cash with my debit card. The phone stopped working after 25days of purchase without any form of physical or water damage, which means that T-mobile sold a defective phone to me. I took it back to T-Mobile office on 05/06/2015 for phone exchange based on their manufacturer warranty. After being pushed arround by T-Mobile agent, I was told to ship the defective device  to their warehouse, which I did at my own expense.USPS (shipping service) and their customer care agent confirmed that they received the defective device on 05/07/2015. Acoording to their phone exchange policy and the customer agent that attended to me, I was supposed to get the replacement phone after 5-7 business day. But it's going to months now and they never sent any replacement phone and they do not want to honor their return/warranty policy. Each time I called the T-Mobile customer care, they rudely tell me that I should keep on waiting till I hear from them, when I went to their retail office where I purchased the phone they told me thesame thing to keep on waiting, apparently they are not doing anything to replace the phone. I believe T-mobile sold a fake version of Samsung Galaxy S6 Edge to me and they do not want to honor their return policy.