Standard Bank Agent threatens to harrass client with constant calling.

Standard Bank Loan repayment department claims that they did not receive the April payment from my mother who is the surety on my student loan. But they sent an sms on the 19th of April to confirm that the money was debited from her account. They called to make arrangements and my mom informed the lady that she cannot confirm at the current moment when she will have the money but she will make a plan to get it and pay. She responded saying she would call my mom daily to harass her about making the payment. This lady the told my mom that "she works, gets paid and should be able to pay the money". And my mom told her that she has other expenses too and it was unfair and unprofessional for her to say that she works and get paid... She asked if that is what Standard Bank tells them to tell clients when they don't get their way. When my mom asked for her to tell us her name, she rudely hung up the phone. Please assist because we don't even have her name to file a formal complaint and she is not at branch level. My mom does not need to be constantly harassed by Standard Bank agents when they are the one at fault. They have been constantly calling me for the past week more than once or twice daily and finally I got to be home with my mom so they van speak to her. My mom is an ICU professional nurse and ICU is demanding, she does not need to be harassed by Standard Bank Agents.