Bad customer serivce

i bought a pair of shorts on Thursday but they didn't fit,than when i want back to exchange them the following day for a different size complete with my proof of purchase they told me that they wont be able to assist me because i didn't have the thank you card that was swiped when i was purchasing,but what really made me angry is that i never wanted cash back i just wanted to exchange for another pair.i don't see a point offering customer's the thank you cards but than they don't explain the terms and conditions,on top of that the manager of the store was so rude,and the head office wasn't helpful.