Bad Service - Promo Code

I used the promo buy 1 get one free burger but was charged double for my order I immediately called your call center and Max said he cannot stop the order but will speak to management on my refund the next day i followed up and Lihle wasn't very helpful, i produced the screenshots of the promo code and she can clearly see that we had a promo code, but still charged us almost R300 for two Burgers that was on promotion, she refused e refund and stop replying to my messages or refused my request to speak to management, Max confirmed the error from their side but we had to pay the bill, very unprofessional from the call center, times are tuff and ordering through Mr Delivery should be a treat not a *******....very bad service... bets to stop using these types of services ripping people off