Harassing their client

I am trying to close an old credit card account for my daughter. She is regularly out of the country for business, and asked me to call the bank to close her account. They are charging her a R25 every month. She paid R100 now and again, but then they call her again. I called them this morning, but they refused to close it because I do not have authority. She must now send me authorisation to close the account. In the meantime, they are charging another R25 and calling her three or four times a day! For R25! This is harassment!