How to get a refund

I purchased VPN but for some reason it refuses to work on my PC. I have reloaded it several times but to no avail. I have given up and now want my subscription returned.......but how!!! I cannot find a way to do this, I know it's not made simple for obvious commercial reasons, but I will not give up until the money that I paid for something that doesn't work is back in my account. Can anyone help?