Disastrous return/exchange service!

Bought a dress for my daughter on 30 Dec 2018, only it was a small make and was too small. Went back a few days later to return or at least exchange it. They refused to help me as I lost the slip while removing said item from the bag. Didn't help that Pep Ottery told me to go to the store where I had purchased it( Kenilworth Center) as they said I was given wrong info and also refused to exchange or refund! What must I do with this dress now?? I spent petrol up and down to stores and stood in lines more than 20min for nothing! Was on the phone with customer care twice and was on hold for more than 15min and still never spoke to anyone there! This is the worst service I have received from any store. I have in the past exchanged items here without a slip and was never an issue. The tag is still on the dress for Pete's sake! I wonder if they will even respond to this complaint...