thank you !!!

Dear all, I have parked on 30th of March 2017 in Napier Parking in Milton Keynes and after carrying out the first transaction I saw no ticket coming out of the machine to display on my dashboard. Straight away and to make sure I paid, I made a second attempt and to my surprise I received two tickets, which means I have been charged twice. I didn't hesitate to e-mail Napier parking with pictures of my tickets and all I have received as a response is that it was my fault for not looking properly for the first ticket as according to them the machine was working perfectly, and no refund will be made. It was an all day price of £8, so I ended up paying £16. I feel ripped off and have already raised it with BPA (British Parking Association), but I am open to any advice. Thank you, Veganfluff