Forced to tip more than what we had

On the 24/01/2018 we went out for lunch, we went to mall of africa spur and we were served by Goodman when we finish eating he brought the bill and it was R697 and we gave him a tip of R13 our budget was R700. When he saw how much the tip was he was like"TJOO guys R13 only " and he didn't add it when swiping our card. So I want to find out if it's a must to tip your waiters and if it's a must how much do we have to give them or is there a specific percentage that we have to tip, I was really disappointed