Bank account changed

FNB changed my bank account from a Smart account to a Gold account without authorisation or my permission. To my suprise I got an email to say that my account has been changed to a Gold account. I also got am sms to say that my new card is being delivered. I did not ask for my bank account to be changed as the Gold account charges are quite expensive. My account kept going into a negative because of the Gold account bank charges and that is why I changed to a Smart account, because it is affordable. Please have my account changed back to a Smart account and the new bank card cancelled.