Fnb **** , deducting money without permission

Hi

FNB has been debiting on my account for the past few months With( bis/int 1 on true tiering ) i don’t even know what on earth is that for cause I don’t owe them anything. They are deducting their monthly fees with more extra cost but still debit my account with that bus/int on tiering and no one explained to me what is that . I want my money back

Please assist and clarify this