Can not join Gym

I recently wanted to sign up at Virgin Active and was told that there was an outstanding amount of R900 on my name, when I joined the Gym in 2006. They said that I must first settle that amount before I can join. I have no recollection of ever owing them money or have ever been phoned telling me about the outstanding amount, they can also not supply me with proof of me owing the money. I would love to join the Gym but I am not going to pay something that i am not aware of or have any proof of let alone something that is almost 9 years old.