Bad service all around from management to sales staff

About 3 weeks ago i bought a Guess dress ar Edgars i have since misplaced the slip but the tags are still on the dress. I then went to the store asking can i get a gift voucher or exchange for something else. The manager very arrogantly said no. I then asked her what i should do with a R900 dress that does not fit her response was its not there problem. I have never in my life heard you cant exchange a garment without a slip that id still in its original order.