Dis-Chem Pharmacies - Exchanging baby formula

I have a baby with eczema and she has always been using Similac total comfort and now they have changed to "Gold ". I bought it and I wasn't aware if was going to cause an allergic reaction.

I wanted to exchange the formula but I was not allowed to because of the policy. I bought the formula a week ago and I was told "what if it has expired"

I buy my baby stuff and dischem every month and I am not sure I will be doing that anymore