Poor Customer Service

I have an account with Dunns, i went to buy at Ackermans in Eastgate with my Dunns card for my grand son who's now 5 months old. I bought a cream white winter one piece sized 12-18 months. My daughter took it to her home and never tried it on him. It was very cold, when my daughter wanted to dress him with it, to her surprise it was too tight for him asif it was 3-6 months item. I went to Ackermans to try and change for the right size, bear in mind i bought on credit. I didn't keep the receipt, and the price ticket was removed. I went to Ackermans because i bought on credit to my amazement, i was told no return if there's no price tag or receipt even if the transaction is on my credit account. I know Woolworths exchange or refund with a Woolworths voucher, even when these things, price ticket and receipt isn't available. How do i keep something with wrong sizing that i have to pay R220.00? This is a pathetic customer service and the other lady, an employee told me with pride that it is their policy and there's nothing she can do about it. I realized that the item i bought from Ackermans, was incorrectly sized and i don't think it's fair for me to go through this. Polocies are man made, but the thing is: the sizing is incorrect.