Incorrectly debited

I signed for a gym contract with Planet fitness on Discovery vitality terms for a monthly debit order amount of R119. In 2016 Planet fitness increased the debit amount without advising and upon enquiring I was told it was Discovery's responsibility.Planet fitness have now debited my account for R599.00 without consulting. After phoning the gym I was advised they would not refund the amount.The contract I signed for was for a vitality amount and if vitality was no longer active the contract should be null and void. The gym cannot debit my account as they see fit for amounts I have not approved. I want my fund rightfully returned to my account. The contract was emailed to to me does not make provision for planet fitness to debit clients accounts at their discretion.<br> Disgruntled<br> <br> Didi Sehume