MTN only have *********** STAFF working for them!

Sign up for a product on promotion in November. From January 2023 MTN have been billing me R800 for a R299 product. I made an inquiry and MTN said it will be fixed. Feb 2023,nothing was fixed and again the money was taken. Went very high up and again the promise was that the price was fixed and a credit was passed. March 2023,and again I was billed the wrong amount, no credit was passed. How can a company like MTN not sort this out. They have nothing but *********** staff.