Pressed to pay extra charges for their mistake..

Bullying by Massbuild Credit department.. I was billed on the 8th Jan 2025 to pay my accounR427. 07. On the 10th I paid R430. 00 at Checkers Kroonstad.. And between 13th got anothenotice to pay R447. 07. I ignored that bcs I already paid.. Soon after followed by many calls requesting me to pay 'shortfall of R20. None of the callers can explain why should I spend Petrol to go and pay R20 that was billed on my account after I have paid. But I get pressed to go and pay R20. I made a request dt once, I am billed, no one should call me to ask me when to pay bcs it's my resposibity to take care of my bill. How much it cost to make ds calls. I will not accept to be charged extra bcs someone did not pick it up that my account was already paid on the 10th. Thus coming from such big company is bellow and leave sour taste in the mouth. People must take closer look at this silly charges.. Thank u