Harassment overload!!!!

What can I say that has not been said before!! This has got to be the most irritating and persistent company I have ever had the misfortune of dealing with!!!! 3 Years ago I paid up my Absa Credit Card, then the calls started!!!! The more I explain I have paid this account, the ruder and more persistent they become!!! I have even had a few of their operators put the phone down in my ear when I tried to explain the I have already paid that account!!!! One of the operators admitted to me that my payment reflects on their system and that it was wrong of them to keep contacting me and that he would sort it out for me - that never happened!!!! When I ask to speak to a supervisor, I am given an e-mail address. The e-mails never get answered and I am now beyond tired of this harassment and would love to know how I can take this further.