Refuses to take duplicate gift and give a giftcard

My son received 3exact sets of hotwheels for his birthday. I have been in to return 2of them. I understand that I do not have a receipt so do not expect cash back. However I do expect the value of the items to be loaded onto a giftcard so I can use it in the future. I have been told that they will not do that I need to choose something else. This is unacceptable as he has now received lots of presents and does not need anything now. I cant believe you expect me to phone the mothers and ask for a receipt so I can return their presents. This is shocking and I definitely will not be back in a hurry!!!!