Dissatisfaction with Order

I ordered dog food that was meant to come with a free blanket. The order was delivered in a timely manner but the blanket was not included. When I contacted customer services via email , I was informed that I was meant to select the free item in checkout. I was not aware of this, neither did i see any option on checkout. I cannot understand why they will not just send the blanket as advertised and in the spirit if good customer care. Thought they had good service, but starting to doubt this now.