Faulty website allowed booking that was not available

I made a booking on the 26th of April for the 27th for quad bike riding. My friend and I accidentally double booked and I tried to cancel it. All my efforts were not fruitful therefore we decided to cancel hers instead and keep mine. I then found out that my booking was pending, the booking time that the website allowed me to book was not available yet I somehow booked. I have been seeking assistance for more than a week and the people are sending me on a run around. I want my refund