Subway Sandwiches & Salads I paid them and they robbed me! Hapeville, Georgia

I went to the Subway on 519 Central Avenue in Hapeville for lunch on May 13, 2011.  I purchased two 6 inche orchard chicken salad sandwiches. 

It totaled to $7.49.  I gave the cashier $20.00.  He only gave me $2.51 and no receipt.

When I noticed the amount he gave me, I knew something was wrong and asked him, "didn't I give you $20?"  He held up a $10 bill and said "you give me this."

I asked him this because when I arrived at Subway, I had just left a stressful situation.  Given this, my mind wasn't fully aware of how much I gave him, but I believed to have given him a $20.00 because I did glance at the bill prior to giving it to him. 

And I was right.  When I returned to my residence, this was confirmed.  The person who gave me the money said that it was $20.00. 

I believe that the cashier knew this and chose to keep the money rather than give me the change that was due to me - which was the $10 he held up and claimed I gave him.