Dialdirect taking money from my account

I took car insurance with Dialdirect after experiencing disappointment with poor service and inexplicable debits from another insurer. I’ve been paying the same premium for the last few months and then without any prior written notice on the 30th of October I was debited a different amount which was R110 more. I contacted my bank and asked them to reverse this debit order because it was unauthorised. Now Dialdirect has written to me stating that because I reversed the payment it means I have no cover. I am not paying for something I don’t know so they must explain to me what I’m paying for. Who authorised the payment? If this is how they operate I cannot trust them anymore!!! I work hard for my money and will not allow them to just take as they please. I am beyond livid!!!!