EFT payment not accounted for in monthly statement

Ackermans account division is the worst cause this is not the first time it is happening to me and last time it affected my credit score. I paid 90% of my account on 24 December 2021 and a week later I get sms that I still have to pay my monthly installment account. Fine I pay it and now when I get my account statement my 24 December payment is not reflected. I call their their account department today and I am put on hold for 4 minutes. Even sent an email with proof of payment last still no response. Already you owe me money cause my account is over paid. Such when people do not do what they are employed for