Over Billed

I had a medical aid with bonitas, where they knew me and my spouse are unemployed. i used to pay R798.00 per month. I decided to terminate my contract with bonitas August and that is when bonitas told me i owe bonitas money because i did not submit documents to prove me and my husband are unemployed. I asked why am i being told this now because every time documents were needed they will send an email and i did not get a response for that. Now bonitas says i owe them R2,931.00 which they say its a short payment for July and July a debit of R798.00 was debited from my account by bonitas. I now work as an intern and i earn R1980.00 and bonitas says i should pay them R977.00 per month until i finish paying them. My question to them was why do i have to pay that amount if my debit went thru and why do i have to pay that amount while i was never told i have to submit documents before they decided to default my account to a higher income batch. So now i don't even know what to do with this burden from bonitas. because according to my knowledge i do not owe bonitas anything as the debit went thru of R798.00 which i have been paying every month. Thanks.