Momentum Health Payment Dispute

I cancelled membership effective 31 August 2019 owing to compulsory membership of employers medical scheme. I called the contact centre on more than 2 occasions to confirm that the debit order would not run as membership is paid in advance, therefore I paid for August in the month of August. To my surprise, the debit order ran on 1 September. I called Momentum after reversing the debit order as I believed it was done in error. They advised that my membership was paid in arrears, now communication to me is conflicting from Momentum. I received an email stating that my membership will lapse if I do not pay the outstanding (I terminated my membership on 31 August 2019). 1 October, Again I am debited by Momentum, again I reverse the debit order. I called the contact centre and the agent explained that the membership was part of corporate membership and paid in arrears and transferred to own scheme at which point it should have been paid in advance, this time i got a reference for the call, Reference ***. I informed that I will not pay any premium as this was not was was confirmed upon termination in August and subsequently upon follow up calls in August. I was told that my query would be escalated and I would received feedback within 3 - 5 working days, this call took place on the 2nd of October. it is now the 22nd of October and I am still waiting for communication.