Declined purchase that I'm been charged for

I tried to make a purchase at PnP via MRD using Mobicred. I received an SMS saying that the purchase was declined and that I should contact the Mobicred helpline for assistance. A couple of weeks later I realized that the declined purchase now appears on my Mobicred statement. I called them to enquire about it but I was told that the transaction appears on their side . The order doesn't appear on my MRD app and even the order given to me by Mobicred can't be traced by MrD. I'm told that I'll have to pay the money even when I never received the order nor an order number from MRD. I cannot be assisted by MrD as they need an order number or a Wi-code of which Mobicred cannot assist me with