Old stock

I bought a Yardley mascara from Fourways. Although it was sealed when i opened it to use the contents were dry. I returned it to the store with till slip however they refused to exchange it. The only reason given was they do not exchange once it had been opened. When I explained that a fault can only be found once opened they just said there was nothing they could do. this policy does not make any provision for defective stock which should be refunded or exchanged.