Bad attitude and threatening voicemails

One of my debit orders did not go through on my account. Later when scanning through my bank statement I see a debit order that has gone off with reference MFCArrearsInstallment. I assumed that the account was up to date again. A lady left a message on my phone saying that she would not allow that the account be left unpaid. At that stage a paid R1000 to the account, thinking that there might still be something outstanding (like a late payment fee) I missed a call from an unknown number today and then got a voice mail from the same lady which said the following: It seems to me that you are avoiding my calls and this is unacceptable. There is still an outstanding amount on your account. I see that you paid R1000 to the account. Who gave you permission to do this? You have no right to do this. I am the only one who can make payment arrangements. Contact me immediately so that you can pay the arrears.\ All of this was said a very rude and judgmental tone of voice. I tried phoning back 3 times. Holding on for at least 10minutes at a time