Petty and small minded

I am in arrears on my 15 year old home loan to the amount of R1200, and they are harassing me on a daily basis regarding this. One lady told me it is so I can maintain my good payment history, which is obviously meaningless, because if they had looked at my payment history they would have seen that for the first 14 years there was a lot more paid in than necessary, but that is unimportant to them. Being in arrears is not where I want to be, but as I am self employed I never know what my cash flow will be like, especially in these tough economic times, so I cannot make any payment commitments. They also seem to lack the mental capacity to figure that the value of my property has increased in the last 15 years, so the original bond amount (only 50% of the purchase price), is insignificant in relation to the current value. The outstanding amount is only about 4% of this value and the arrears only 0.4%. If this was a new 90% bond and I was months in arrears I could understand their concern that they may lose money, but the chances of that happening with me is absolutely 0. Instead of taking the above into account they choose to harass and alienate me. I can't even speak to anybody at my branch any more- they just refer me to their call centre !