Disappointed with baby clothing size labeling

On Sunday afternoon I bought a baby winter grow for ages 12m-18m at Keywest Ackermans. I confidently threw away the receipts as well as put the baby grow on the wash. To my surprise when I tried to dress my 9 month old baby boy , the buttons wouldn't even close; it was too small!!. I am an unemployed mother of two and every purchase I make is seriously thought of as money is hard to come by. I spend R200 on a grow that I can't return and not even use. I am extremely disappointed with your product Ackermans. Had I bought a size 6-12mo it would be understandable. But this was pure misrepresentation of your product. Am a disappointed poor mother who can not afford to throw away R200