Underpaying is called missed payment

I made a payment last month which was lower than the prescribed one and then I later I just received an email saying I need to pay more worst thing I call their center cos I got a negative credit rating as a missed payment I asked for their help they say what's done is done they can't undo it I have been meeting my account requirement all these months and one month of a lesser payment which was R137 underpayed I'm reported to credit bereau as a missed if this is how customers are treated ai khona thank you very much and bye bye worst treatment ever and the fact that you have ruined my credit score