NUDEBT - FINAL DEBTS WITHOUT SUPPLYING PAPERWORK

I keep on receiving DEMAND FOR PAYMENTS AND FINALD NOTICES, without any paperwork attached. I am sure that we paid this, but without paperwork, I cannot make sure about it. I have requested this 3 times now. They keep on reading my mails without any response. This morning, I received another Final Notice. How can they expect payment from someone if they do not send paperwork on said debt.