Planet fitness turns a blind eye when their sales reps forge contracts to book a profit

I joined the gym under a student membership. When the contract was left with a month to expire I told the sales rep that I will not be renewing the contract since I will be over the age of 25 so I won't be qualifying for the student contract. The sales rep came and told me that since I joined when I was of age. I renewed the contract and to my surprise after a couple of weeks I received a call from another sales rep asking if I work at eskom and I said no I didn't. Then he told me that the contract I had signed was only for eskom and discovery beneficiaries and I don't fall on either of them. The sales rep then said that I won't be able to go to the gym because of the invalid contract. And now my surprise planet is trying to use the same invalid contract to say I owe them money even though I was told that I won't be able to come to gym anymore. I tried to go to the branch in emalahleni to enquire , I asked for the contract to prove that I owed them money. They showed me a contract that was written student and had my signature which I was aware of but on the same page it also said eskom employee with a signature that looked like mine but I never signed. So I am disappointed because why does a respected brand like planet fitness promote their sales reps to forge signatures and still try to make people pay with an invalid contract