Exchange not allowed

After taking out my kids layby I realised that one of the pants don't fit so I went back to power clothing in kagiso Mall to exchange for a bigger size only to find out they don't have the same pants so I took a Jean for him. I asked my daughter to return the jeans because my son don't like those pants. Only to be told we already exchanged so we are not allowed to change again. There slip doesn't display how many times you can change even if you read there terms and conditions these nothing about this. I've sent an email and still haven't received a response.