The `confused records' scam is just one of the many ways to lie to a collector to delay, reduce, or eliminate payments. In this case, you claim that another agreement was made with another collector when you called earlier. The other collector must have made a mistake in the process and put your information on another case. The larger the agency, and the less adequate their automated system, the easier it is to get them confused. An agency with a good collection system is harder to fool because the `social engineering' tricks don't work as well.
The concept of creating confusion is a powerful one, and its power increases with the size of the organization. Almost all large organizations have built-in confusion factors in their collections because there are people who are working on the same collection case that have never even met each other. If you say `Lucy told me this' there is likely to be some person named `Lucy' somewhere in the organization, and they will be faced with chasing Lucy down if they want to clarify the dispute.
Another side effect of confusion is that it tends to get your debt placed into a holding mode which it may never leave. Most collectors are a bit overworked, and like everyone else, will seek the path of least resistance in collecting their bills. If you resist and there are always other debtors pending who resist less, why waste time on you?
The defense against all of these confusion tactics is becoming very systematic about your pursuit and stay within the bounds of the system. If the debtor tells you about Lucy, explain that you are not Lucy, but that they still have not made payment on time. Explain that you will be sending this case to a lawyer for legal action within 10 days unless you get the payment before then. Give the proper impression that you are at the leading edge of an avalanche that is coming towards them, and that nothing they say or do will stop the process except sending you the money today! If you don't get confused, they will pay your bill and not pay the one being collected by the confused collector.