MBD Incorporated harassment

I have been harassed for 5 years by MBD Incorporated. I was retrenched and had Insurance cover on my credit card which was paid. Unfortunately I then had to make payments theteafter per month to pay off what was still left. After we agreed on a specific date where a payment will be made they still start phoning you from the 5th of the month and SMS you.. This occurs atleast 5 times a week and sometimes twice a day as early as 6h30 in the morning. I have never defaulted on my payment. When you look at their statement, It is if great concern that it is totally shocking to see that they not only earn intetest but also charge you for every call and sms they send. I have phoned numerous senior people and I was told by one of them just to ignore the sms and not to answer the calls. It is now a case of total harassment. I have noticed that many people have the same problem with them. What are your rights regarding harassment and when will this debt be written off?