Feeling Disgusted and ****med. Employee giving business a bad reputation

Paarl branch. Went there for breakfast on 29 Dec 2023 @10am. The restaurant was not busy we still had to wait approx 25min for our simple breakfast special. Our bill came to R282.00 We opted to pay R310 to incl a tip. My son requested to swipe for R100 and I requested to swipe for R210. Instead, the waitress swiped us for R120 and R220. My son did not ask for a slip but I did. That's when I realized that she overcharged both of us. Only once I mentioned the overcharge did she quickly say, I will get you the R10 cash. No apology. Asked my son to check his payment. Only then did she refund the R20 overcharge to him too. Her behavior got me thinking, how many times has she done this? And she was the manager of the day too.