Planet fitness cancel beneficiaries contract after two months

In August 2019 i visited Planet Fitness at Carnival mall and the sales lady told me they have a women day special for me and my sister's daughter.She was fully aware that she is not my daughter but told me she could gym under my contract until she is 18years old.I signed the contract and submitted all the documents required.End of September they blocked my sister's daughter and told her that her contract have expired.I demanded to speak to the manager and was coldly told that it is against the companies policies because she is not my daughter and then she can't gym under my contract.I explained to the manager that the sales lady knew that she is not my daughter and still given me a contract.He then told me sorry this is against the companies policies.I also explained to him that this was a breach of contract from their side as i was ******* into signing a contract under false pretences.He also said she is off sick and cant defend herself.I said that i then want to cancel the contract and he said there will be cancellation cost involved.Why must i pay the cost as this is not my fault?He also treated me coldly and did not even said he will speak to his sales lady and give me feedback.I am very dissapointed with Planet fitness.