Incorrect premiums deducted/ paid

I changed my bank details from capitec to standard bank. for a reason unknown to me cell c decided not to do these changes on their side. debit orders didn't go off and my account was suspended. i paid the outstanding amount and cell c also decided its ok to make a further debit from my old account which was meant to have been changed. my cell monthly premium is R307. i have paid R2223.00 and they deducted R1667.96 . all these monies for missing 4 premiums. I need n explanation of what is happening and why is cell c disregarding my instructions and doing as they will on my accounts.