Bad attitude and service

We bought items at Markham on 23 December 2015 on my account with my fianc?. On the 24 December 2015 he went to the store to exchange 1 item because it was smaller. When he got there they took the item and he was requested to go find a bigger size. He took the item to the cashier, the cashier credited the item back into my account and there after he said referring to another cashier next to him that he made a mistake. The both laughed and told my fianc? that he can't get another item. He requested that they give him back the item they denied and called a security. He was never given an item back and no slip to prove that item has been credited back. He left the store after a while they called him to day they now have a solution. I am very disappointed with the service that employees of Markham have displayed.