Ordered iPhone 15 pro through Store and getting charged for 2 devices

Hi I ordered iPhone 15 pro while color form Store and it seems they dont have the same color so they recommended me with silver color, and i said ok and got the siliver 15 pro, they alsi mentioned that the previous device ordered will be cancelled and i trust them and left the store. Now after a year i found that i am being getting charged for both the devices. i called Tmobile support and they are saying it is been a year i processed those devices so they dont have record and i have to keep on paying for both devices which i dont have. so i am feeling that i am getting scammed by Tmobile.

So i need your help to resolve this issue and recomend me what do i do to get my money back and cancel the ongoing payment.