Embarrased at my work place

On the 23/02/2014 Wessels sent by Norman Bissett and Associates came to my work place to collect debt that prescribed. This debt collectors has been harassing me calling many times a day at work, on my cell and now they come to my work place. I have informed their consultants to stop calling me and close the file as it prescribed but they continue harassing me. I have also asked them to send statements that show last payment till now I haven't received none of the statement. I want Norman Bissett and Associates to stop harassing me over prescribed debt and to close my file.