My free Coffee

On my way into work for back shift Friday night I stopped at Tim Hortons to get a coffee. I only got an extra large coffee and I paid with a five. I SHOULD have gotten $3.27 in change but got $8.27. I told the lady at the counter that it wasn't right...she apologized and handed me a 10 dollar bill. Okay clearly math was clearly something they skipped during orientation. The more I tried to explain the more confused she became. In the end I was going to be late for work so I took my coffee and the $18.27 she insisted I was owed and went to work. Honestly I don't know how people like that stay employed ANYWHERE!