Eskom keep on sending electricity bill even though we changed to prepaid.

My 80-year-old father changed his electricity to prepaid system in 2017. Eskom employees came to his house and install the new prepaid system and took the old meter box with them. Even though the system has been changed to prepaid and he had been buying prepaid electricity vouchers from July/Aug 2017, he still receives the bills from Eskom every month. He does not owe Eskom any money. He also receives SMS’s and phone calls that he needs to pay. On Friday 5 January 2024 at 09:37 he received SMS from the following number + *** with the following messages: “Minimum payment of R2 259.19 required on your Eskom acc for your outstanding balance: R13 555.15, Send proof to WhatsApp ***. ***”.