payed cash and i get gift card for refund

hi, i have purchased shoes for my daughter last week thursday only to find that the size was too small. Went back to the shop on yesterday to exchange but didnt have the till slip as it was misplaced. When i got to the shop i didnt get the size i wanted therefore i requested for a refund. They said they cant refund me because i dont have the till slip they can only give me a cash card. At that time a had to get another pair from another store because they didnt have the type of shoes i wanted. I asked them if they can get a copy of the slip because i used my cash/ poits card. They were able to trace the slip but they insisted that they cant refund even though they have proof. What i dont understand is if they have the proof on the system why dont they print it out and requested for my ID copy to confirm that im the one who is doing the exchange because the poits card have all my information. I found it so unfair that i gave them cash and i get a gift card.