No Exchange

So my husband bought me a dress at Truworths as a gift, i looked at the size and was correct. Two months later i try on the dress as i want to wear it for a very important event and find out the dress fits but my girls are all over the place, i take it back to get a bigger size and the cashier refusebto exchange the dress with all its tags and slips. I tell her i didnt know their policy but she wanted be to buy a second dress as she refused to exchange it. I would understand if its a refund but i just want a bigger size. The dress is over R700 what am i suppose to do with such an expensive dress that i cant wear nor exchange. I am very disappointed with the service, when they get a sale they dont ask a single question but if you take it back you get attitude. I told my husband to cancel his card as this is unaccaptable.