Le Morgan debit nightmare

I bought their products worth R40000.00 with a total installment of R1500 monthly deducting on the 15th monthly and during 2021 November their debit order did not go through as planed and I paid the full amount within the month of November 2021. The only thing I omitted was the reference number. They then listed me as a slow payer without informing me. When I seek for credit somewhere I was alerted of this gross nigligence. I imidiately called and sent the prove of payment and still now my credit record reflects bad because of them. I pay them every month bt they have the nerve to treat me this way. I called them several times to rectify and always I'm answered by clueless consultants who acknowledge the receipt of the prove of payment bt don't know how to remove the errors.