Poor customer service

I purchased a novalac premium formula stage 2 on friday november 29, however this was an incorrect product as my child uses the stage 3. I did not notice this when picking it up. I discovered that it was the incorrect one so on Monday December 2nd, I went back to dischem umhlanga gateway. The manager on duty stated that I cannot change it for the correct one or have a refund. He just refused and I had to arrange another lot of money for the correct one. I am now seeking a refund for the incorrect product. The manager could not answer as to why he could not refund or return the product. He then referred me to contact Novalac directly. I feel this is really unfair because I paid you for the product and not your supplier. The product is still sealed and nothing wrong with it. Can you please get someone to sort this out for me urgently! Also I called your call centre earlier this week and I was hung up on. Can this also be looked into? I will respond with my number upon your reply. All of this has caused alot of stress and inconvenience.