Mama samba overcharged me and they don’t want to refund me!

Our bill was 1140 including tip,me and my friend split the bill,my portion was 350 and hers 790. The waiter tapped 790 twice,we think it was on purpose cause there’s no way 790 x 2 can amount to 1140. I then spoke to one of their managers they apologized and promised to fix it and never did,the promised me to refund me my R440 but even now I’m still waiting. Poor service indeed,I’m thinking they’re in this together overcharging customers for their own good.