Harassed daily for money already paid

I have been harassed daily by your call centre agents for 2 weeks now for monies already paid. I have emailed the proof of payment to three different individuals and yet I am still being called up and asked to pay the outstanding R500. Two payments were made, one from my and one from my husbands accounts with the SAME reference number. How difficult can this be to track considering I have sent the proof of payment through three times??? I have asked to speak to a manager and they are always in "meetings". Ridiculous. If I see your number come up I am simply cutting you off now. I see there are many bad reviews about your company. Time to get your act together don't you think??