Airtime purchase

Hello I am a Mrp customer. I paid my Acc in full in July 2020. Then In August I recieved a statement via e-mail. The statement showed that I purchased a R500 Airtime of which I kno nothing about. I immediately rep**** to the e-mail and made them aware of the purchase which was a ****. I was told to send an affidavit together with my ID copy of which I did. I even used the whatsapp a service where I was told to send those documents again. After that I have never recieved any response Except for calls from debt collection to remind me to pay Acc. I am worried as this affect my credit rating.