Nedbank deducting Greenback funds without my permission!!!

I am furious with nedbank as before they deducted greenback funds from my account without my permission where as i had to cancel it and still had to pay it as well... I dont use my nedbank account for a while now and when i recently checked my account i noticed that nedbank has been deducting greenback funds from my account once again leaving my account in a minus which i think its wrong and unfair towards me...i think its purely theft!