battery exchange

On the 25/05/2020 I bought a car battery at Queen motor spares. In august 2020 my car has a problem , always does not want to start up until I took it to the mechanic. Mechanic checked and confirmed that there is nothing wrong with a car the problem is with a battery. I went to spares and the Manager there told me that the battery has got no problem and I must go and do exchange at Willard where they ordered batteries , imagine I know nothing about Willard I bought it from them. He said he will not make exchange. Please I need your assistance I don't want battery I want my money back so that I can go and buy new battery , seemingly they are selling old batteries.