call centre harassment

My father is an 80 year old pensioner. After my mom passed away last year, my father started receiving calls from Brooks and Luyt due to an outstanding amount on a credit card that he was not aware he had. I finally managed to speak to Brooks and Luyt and made a payment arrangement to pay off the outstanding balance on behalf of my father and I have paid the first payment in line with this agreement. I have subsequent to that and despite the fact that they have received the first payment received on average 5 calls per day from the very same call centre following up on the payment arrangement. Only when they get through to me do they realise that there is an arrangement in place and end the call. I have emailed and provided proof of payment but I still get calls. I ask to speak to a manager or supervisor and the call centre agent just puts the phone down. I am only grateful that I am getting the calls and not my elderly father as this would have stressed him completely. I wonder, if FNB were made aware of this harassment, they would still want to outsource this work to Brooks and Luyt ?