cancelled my policy but debit order went through

I joined oneplan on the 27th of July and from reading my policy and through confirmation by their consultant I has 30 days to cancel the policy. I found myself unemployed within those 30 days and on the 18 August I cancelled the policy. I was told I would pay an administration fee of R100 for cancellation which I did not mind. I even received a sms to confirm my cancellation. Now oneplan has debited my account with over R900. This is in breach of the contract and the Credit Act. I cancelled this policy within the 30 days cooling off period. I want my money back please or else I will be forced to approach the Credit Beareau. I have tried calling their call centre but my airtime gets finished before I even get to speak to a consultant. I am very unhappy with Oneplan considering i was referred to them by a loyal customer of theirs.