Refusal to exchange my girl's trouser

Woolworths Rustenburg really disappointed me, I go there to exchange a school trouser for a bigger size for my daughter that I bought at the Mall only for them to tell me the trouser was altered, I'm like why would I alter nd then want to exchange nd worse I even kept the slip nd price on the trouser, that supervised refused me to exchange even though I repeatedly told her that Mam I jus want a bigger size for my daughter I ddnt temper with this I dnt even want a refund jus to exchange please but refused, so what should I do with this smaller size trouser...????????