Payflex overcharging on certain payments for no reason.

I have been using the service for a while now. I recently had to update my card as the old one expired. My payments did not go through automatically (debit) , I then had to make each payment individually which totalled to almost R2000, if I'm not mistaken I made 5 payments for different transactions. I noticed one of the payments was a higher amount than it should have been. I contacted Payflex via WhatsApp which only assists via a bot which was not helpful at all, I then emailed the support email address. The automatic reply made mention of a 72 hour turn around time which I understand. This was sometime last week and the 72 hour period has passed, I sent a follow up email and I have not received any feedback whatsoever. I have not missed a single payment using Payflex and I find this service extremely unprofessional for not getting back to me regarding a refund. I have 2 more payments which are due on the 1st of August, once these are done I do not think I will be using this service again unless this issue is resolved and there is a easier way to rectify these issues.