Selling faulty Goodson

I replaced two tyres with them on the 29th July 2015, and all I do is drive to work and back(10minutes). On the 20 September I noticed one tyres was flat and took the car back to them, they said they were not able to replace it unless I had insured the tyre with them, not that this was offered at the time of purchase, they claimed there was a slash on the side and couldn't repair it. I will never shop there again, they take your money and provide tyres which most likely have been laying too long and sell it to us poor folks who work hard to make a living.