Nedbank is harrassing me!

I took a loan with Nedbank some time last year. In August the same year I called the bank's collection department to inform them that I was going through a rough financial patch and would not be able to make the total full instalment for the coming few months. Following several phone calls over a long period, I was transferred to a certain manager with whom I made an arrangement to pay R600 for three months. When I informed the manager that I was likely to be in the same financial state at the end of three months she said I should call the bank again during the third month for another arrangement. When I did I was informed that my account had accumulated R15 000 arreas during the three month arrangement. Over a long period of long phone calls I was informed that another arrangement would not be possible and that the bank wanted to make an arrangement on how to pay off the 15k, in addition to my full instalment. For a long time I enquired about how the account got into arrears while there was an arrangement that I wouldn't be able to cover the full instalment beforehand. Several of the call centre agents that I spoke to could not answer this question. A month back someone told me that the initial agreement between me and Nedbank had not been amended by the arrangement and I was liable for any interest accumulated while not covering the full instalment. I understood that explanation but battled to understand why I went through a long process of using my airtime to make an arrangement if at the end it was as though I just decided on my own to pay a portion of my instalment without the bank's consent. At that point I weighed my opinions... Nedbank wanted me to make another short term arrangement - which would cover the 15k arrears and the instalment and at the end of the of which the account would have accumulated further arrears, which if at the time I still don't have a lump sum to pay off would lead to a continuation of the vicious circle. My second option was not pay at all, wait for the account to be sent the legal department and make an affordable long term arrangement which includes legal fees and does not accumulate arrears. I chose to wait out the legal route. I then communicated this decision with Nedbank. Despite this I get calls on a daily basis with the agents trying to intimidate me into paying the full instalment and a portion of the arrears. I keep saying that that is unaffordable for me and ask that my decision be noted in their system that I am unable to make an arrangement with them and as that is breaching my contract with the bank, I give them the go ahead to take action against me as I have defaulted on our initial agreement. I acknowledge that I am fully liable for the loan repayment and am willing to cover an affordable amount for me, and I accept it if that is not acceptable for the bank... and in that regard have asked them to take action instead of inaduanting me with calls every single day. Despite stating that to several call centre agents I still get calls from the bank daily. I honestly feel harrased by the bank and its employees. I know I owe it, but the daily calls over the same thing everyday must Just end!