Shop won't exchange clothes

I was very disappointed with the service I got from Exact today. I bought shorts for my son end of November and could not try them on him as he was away visiting. When I came back I tried them but they were too small so I went to get an exchange and they refused because I did not have a till slip but the shorts still had the price tag. This does not make any sense to me because the store always keeps a copy of the receipt, all they had to do was a reprint but they refused flat out. I jus want say that they lost a customer in me that day. I Know they probably don't care about losing one customer but because I will not shop where my support is not valued. I see a lot of people have complained about the same thing but they did not even bother responding. This is is disgusting actually.