Woolworths refuse to exchange clothing items

I received clothes as gifts for my baby boy and I tried to exchange them to bigger sizes because they are small but Woolworths in Pretoria branch refused to exchange items for bigger sizes because they are saying that the items are not on their system but they still have the bar code. Its two winter rompies and 1 packet of vests. Im so stressed and i really need those winter items so that my baby can be warm this winter.