Incorrect billing

I am having endless issues trying to correct an incorrect billing. I have made endless call and numerous enquiries about the R505 329, 41 bill that my dad received in Feb 2020 that's in arrears which I know for a fact is incorrect. When I spoke to spoke to the customer care supervisor (Nonkhululeko) who confirmed that the billing was indeed incorrect, she confirmed that the bill was R0 in Nov 2019 and suddenly in Feb it was over 500k. My 70 year old father walked to the offices in Florida was told they cannot help him. I need this issue resolved because we want to sell the house next year and must get this sorted out. Account number - ***