STD BANK INCOMPETENCE

I have been harrased daily for the past 5 /6 years by a company appointed by Standard Bank South Africa to pay outstanding monies on a loan account of which I paid in full in cash at their branch in Johannesburg somewhat 6 years ago. I continually tell these harrassers to get the correct information from their client STD bank before calling and emailing me again... I have requested from STD bank to sort the matter, been to the branches on several occasions all the while taking leave of absence from work to do STD banks job for them but to no avail nor a response from STD BANK. When calling the various loan departments it is said to me that a manager is not available to speak with, then get transferred between various departments only to be told to call a different number again as they cannot transfer my call in house either.... My credit rating is now not where it should be and cannot apply for credit thanks to the incompetence and lack of client assistance and support from STANDARD BANK... I beg of you to please assist me in this matter, much appreciated and thanking you in advance