Refund not paid in full

Today I went to food *****s Market in Boksburg north rand road. And I bought a couple of items. But when I got to Checkers I realized that some stuff were cheaper there. So I returned the Leg of lamb and olive that I bought from food *****s the lady who was assisting me refunded me but didn't give me the full amount. My change was supposed to be R284. 60 but she gave me R184. 60 I realized that when I was paying tolls on my way home to Mpumalanga. I somehow feel that she did it on purpose. Because how could she have missed the amount with a while R100.