Incorrectly Billed and No assistance provided

Hi, I took out a 10MB fibre line for R499 for 24 months with Telkom in October 2020, i received the 1st 3 months free as per the lock-down special. As of January i was billed R799 each month, i called customer care, went to 3 stores, spoke to so much people, but no one seems be able to assist me with correcting my Bill, absolutely shocking at the client after sales, i have been paying an extra R300 each month which is affecting my pocket. Not to sure what to do from here, Once this contract expires, definitely going to cancel as it this of no fault of mine.