How can collection agencies put entries on your credit report if you never 'owed' them or got credit from them in the first place?

Collection agency buy or get assigned accounts from different kinds of creditors who you may owe without realizing it. Examples of these kinds of debts include bad checks, debts owed from medical services, defaulted leases and others. None of these debts are typical of the kind you undertake willingly (like a credit card account). But they still can be legitimately owed by you. You would need to track down the source of the collection account, find out whether or not the collection agency has your identifying information. If not, then you would need to investigate to determine the nature of information being reported against you. It might be that you are the victim of identity theft.