Charged twice for 1 trip

On the 17th November I created a profile for my mother on the Taxify app, added my own banking details on it and paid for a trip for her going from Bryanston to OR Tambo Airport using my card and the promotional code as she is a first time user. Upon arrival at the airport the driver made her pay R340 cash. I contacted him straight after my mother alerted me and he said he would request a refund for R340 to my account as he made my mother pay the full amount cash and the app made me pay a lesser amount with the 1st time trip discount.... hence making us pay double for 1 trip.

To date I have not heard from him or received our refund for R340. His phone is now on voicemail. Please refund us our money?