Disappointed

I was so disappointed by the markham team in forest hill,centurion.I had bought a t-shirt for a friend as a gift for a birthday.the t-shirt didn't fit and I decided to go exchange it where I bought it in forest hill.when I got there I told the cashier that I would like to exchange the t-shirt for a bigger size,the cashier asked me for a slip,I then told her I did not have the slip since I bought the t-shirt as a gift for a friend,she then called some guy I don't know whether He is a supervisor or what and told him I didn't have a slip.the guy asked where's the slip and if I didn't read that I cannot exchange without the slip.I was also asked when and where did I buy the t-shirt and if I bought it cash or with a card.their questions made me so uncomfortable to a point where I felt like I'm being treated like a shoplifter and why would I buy a medium t-shirt and ask to swop it for a large,it's not like I was exchanging for something different or wanted a gift card I was only exchanging for a bigger size.I didn't even understand cause it's not like it was an old stock,there was plenty of sizes and it's summer stock.please if your policy says no refund exchange without a slip let it be a norm for your cashiers to inform all shopping customers not to lose the slips or have a large ticketing closer to the items that tells us about that.the exchange was done but I felt it was in appropriate since I have been asked so many questions like a ***** while there's other customers there waiting to be served.if other stores can exchange items for their customers without hustle why would markham be difficult