INCORRECT INFO SOLD

I joined Planet Fitness in Westwood mall before the gym was even built, they were selling the contract at R2400.00 for 12 months, that was the only amount and there would have not been any further bills thereafter, in August / October I see my account was debited with R400.00, I called the call centre and was advised that thats an admin fee, when I took the contract I was informed that the R2400.00 was the only amount payable and thats it... the lady says It states in the contract that theres an admin fee of R400 applicable, which I think was totally unfair, because when they were selling these contracts nothing was mentioned and we were told that the R2400 was it and there was no hidden fees, so why was my account debited with R400.00?????