Harrasment and threats

Hi.<br> <br> I just received a visit from a DMC representative at my work place demanding that I sign an acknowledgement of debt. I have not made arrangements or acknowledge this debt. This debt is from 2008 aleady. When I mentioned to him that this is prescribed debt he told me it cant be because they could not find me. No summons was sent to me. What should I do. This is prescribed debt I have told them this numerous times over the phone.