Struggles to Get a rates and taxes account fixed

I am writing this complaint on behalf of my mother.

Below is a brief summary of the situation: She acquired the current property she lives at, after her divorce in 2019. She has paid her account every month for since 2019, as she doesn't want to end up with any legal action against her name. She struggled to change the account holders name on her Municipality invoice. After multiple phone calls and sending multiple emails with proof of ownership, her ID and all the required documents to City of Cape Town accounts department, it was done incorrectly. the City of Cape Town has closed the account she was paying on and created a new account which states that she now owes City of Cape Town a massive amount of R18414.12 (she initially received a SMS stating this amount). After contacting the City of Cape Town telephonically / through email explaining the issue and in the hopes of clearing up this mess, the City of Cape Town consultants bluntly stated that she needs to supply proof of all payments made towards the previously mentioned closed account and that she is liable for this outrages amount. IF the previous account had a zero balance and was paid for multiple years, who do they think was paying this account? We refuse to spend more money to pull bank statements for over two years, just because City of Cape Town messed up. This is an unacceptable way of treating a loyal elderly account payer. We have contacted our ward councilor, in the hopes that this can be settled in a professional manner, but we will be forced to take further action if this continues to drag out and become and issue.