BILLING ON A CLOSED ACCOUNT

In July 2015 my mother paid the settlement figure in respect of her bluebean card (R 17 000), and on the same day she requested that the account be closed. In January 2016 she received a sms and a letter advising that she owes Standard Bank R 500.00. I called in an was advised that it was in respect of charges and interest on charges. They were once again informed that the account was closed in July 2015. Today she received a sms that she was handed over to attorneys to pay R 524.10 or arrange a payment arrangement with LGR Attorneys. I called standard bank I was advised by Nomonde that this was an error on Standard Bank's part and that they will send a letter by 1pm today confirming that the balance is zero. I called again after one and was advised because I was calling on behalf of my mom (who is medically boarded and unable to call), that I cannot receive the letter. This is not the first time that I've had bad service from standard bank. How does one ***** money from a medically boarded person who has been a customer for years? I would like a letter so that I can resolve this matter for mother, as she cannot do this by herself. I will be reporting the matter the ombudsman.