Debt collection — National Credit Systems,Inc. (WI)

Debt is not yours. Im being charged {$2800.00} from a collection company called NATIONAL CREDIT SYSTEMS. I do not know why I have a collection with them. I asked them to send me the original contract so I can understand where this debt comes from but when I try, they ignore me and verify my debt without giving me my request. This collection debt is on my experian and XXXX credit report.