BEING CHARGED DOUBLE FOR MY UPGRADE

I UPGRADED MY MTN BUSINESS ACCOUNT HOWEVER WHEN I RECEIVED MY PHONE BILL INSTEAD OF BEING CHARGED R 1,429.00 FOR MY APPLE IPHONE 11 256BG MADE FOR BUSINESS M, I AM BEING CHARGED R 2,923.16. WHY AM I BEING CHARGED DOUBLE WHAT I AM SUPPOSED TO FOR MY PHONE WHICH WAS ONLY RECEIVED ON 29 JULY 2020. ACCOUNT NUMBER: A***.