Monthly service fee for a closed account

I paid settled my RCS account and sent an email to have the account closed with immediate effect on 08 October 2018. I was provided with a paid up letter on 11 October 2018. On 16 October i receive the statement which indicated i need to pay an amount of R54.00 when i called to check why subsequent to the request to close the account and receipt of the paid up letter, im told its a monthly service fee the account its still open, how do i pay a monthly service fee for a closed account?