Planet Fitness overcharging

I joined Planet Fitness using Discovery Vitality and was told I would get a discount to my surprise R1100 was being deducted from my account instead of R250 as agreed. I told them and was told to leave my ID number by the reception and a manager would contact me and they never did. I sent an email to their accounts and still they didn't assist me. I told them to cancel my account and they didn't. Now they want me to pay until today because they didn't cancel the account. If you don't pay for your account they stop the subscription. Why does their go on even if you are not paying and using their Gym anymore. They also didn't disclose that there is a yearly subscription fee.