Bad and rude agents

I have been contacted by an agent from Hammond Pole regarding my MTN account . This account was handed over to them after I refused payment for breach of contract by MTN. However, I have decided in the end to make the payment and then cancel my contract with MTN once and for all. This agent however persisted in that I must make an immediate payment which I cannot do at the moment. This very agent previously phoned me to ask me if I received her email with my statement which she send a day or to prior. I told her I did not have a look yet. She said she will send it again. I searched my emails afterwards to make sure I did not miss it, but could not find anything from her. Only later that day did I receive an email from her. I am also extremely busy as I have just recently started my own web development and digital marketing business with a really limited cash flow. I do not have time to read any frivolous or non-business related emails. Today this agent again phoned and asked whether I have read the statement, I said no, but the amount she mentioned sounds right. She then basically told me I must make a payment end of this month, which I really cannot do. I, however should be able to make a full payment at the end of October. I tried to explain it to her, but she was adamant that I must make a payment this month. Now I am tired of struggling with inept and rude agents who is unwilling to accommodate me and assist me in getting my account settled. I asked her then to put me through to her supervisor upon which she said there is no supervisor. I know however there is a supervisor, for I had contact with her earlier.