Poor service refused refund

I bought pair of jeans for my four year old son on the 11th but the size is big when I fitted him came to pep jubilee mall on the 14 March 2016 for a exchange but I could find a smaller size but to my surprise I was refused a refund and a voucher..so i am seating with pair of jeans that doesn't fit my son and what am I suppose to do with them..highly disapointed