Poor service

I sent my kids today for exchange the trouser so that she can fit. School trouser the person who assist her said there is no other trouser on the receipt while I bought them yesterday. Both of them now she didn't give the child receipt which is having another trouser that she gave them and still the trouser doesn't fit her now how am I going to return it without slip. I'm so cross right now . Palm springs mall pep. Sies.