Inadequate After Sales

I have purchased a product a few months ago and later realize it was defective. As I am aware it has a gurantee however when I visited the store with my original proof of purchase, I was told they can be of no help as I did not retain the packaging. I was not made aware at any stage when purchasing the product and as such am displeased at the way Autopage handled my query. I will not be returning again and considering canceling my contract