Dissatisfied client

I got an sms that I qualify for a free packet of Huggies nappies. To my surprise I went to the store yesterday and they informed me that my voucher expired which I was not aware of. I bought nappies throughout the year and now that I qualify for a free packet, this is what I am getting. I am not very impressed as Dischem is my no 1 store to make purchases and I don't appreciate this kind of service.