Collection Notice

i received a collection notice yesterday that stated that previous attempts had been made to collect an outstanding debt that I was not even aware of. i moved 3 years ago from north carolina to indiana. at that time a forwarding order for mail was put in place. since then the forwarding order has ceased. the collection agency had no trouble getting in touch with me, why did the creditor? i need to know what these charges were for and when they occurred. according to the creditor, i can get that information but i must request it in writing, which i have just done. according to the collection agency, if i do not settle this debt before the end of this month they will take legal action. i understand that they are only doing their job, but i have received no statement, phone call or other notification of this debt. where do my rights come in. do i have any recourse but to pay this debt before i know what it was for?