Refused to exchange nap pies for bigger size

I went to babies r us in roodepoort on 1/12/2015 to exchange a pack of nap pies bought from them but they refused to exchange it for a bigger size, they say that they have a 14 day return/ exchange policy, I was one day later so don't see what difference it makes as it is not like they will not be able to resell the pack of nappies, o the meantime what am I suppose to do with a pack of nappies which my child can't wear, not like I can help it if my child outgrew the size nappies, so now I am loosing out on my money and sitting with a pack of nap pies which I can't use to me that is just pathetic <br>