Try to close my account, fnb just add in service fee non stop

I'm trying to close my account because I haven't used it for 3 or 4 months. The monthly service fee added up to R1600. I'm willing to pay it off, but just request fnb not to add the more that R400 a mount service fee to the acc anymore so I can close it. No response from fnb. I guess they are waiting for another months service fee to be added to a account I'm not using and want to close