Upgrade and no phone

I need someone to help sort out this mess for me. I did n upgrade online for a iphone 7 plus on the 4th of October. The following monday I contacted one of your service agents to ask if i can cancel the iphone 7 plus and change it for a iphone 11 . She said she would reverse the upgrade. A week had passed and nothing happend. I phoned this week Monday spoke to another service agent to find out whats going on. I see now i am being billed for the new contract but i have no device. Can someone please help me out and advise whats going on?