RETURN OF PAINT

I bought 4 tins of roof paint from the store on 23/03. Due to the time taken to clean the roof and then paint it I now realized that I only needed 3 tins. Phoned and were told that i can only return it within 14 days. The paint has never been opened and I am interested in buying more paint for the house at a later stage but this policy is ridiculous. Will use another supplier in future. Still got my till slip