Not to play Devil's Advocate here... BUT...
I know the co-owners of ULC personally, and they are not the evil conspirators that everyone here is making them out to be. They are simply trying to run a collection business. To my knowledge, they run a pretty tight & by-the-books operation. They judge their employees by the number of accounts they can close, so I imagine that some employees can be a little pushy so they can meet their performance goals.
As for being rude, you would not believe some of the stories that I have heard. These collection agents are constantly yelled at, berated, and verbally abused by people who didn't and don't want to pay their bills. So think about that when you are talking to one of these reps the next time.
Also, the reason that they don't believe you when you tell them that you don't owe them money is that EVERYONE lies to them. That is also why they prefer a credit card to a "checks in the mail" payment.
I had a similar situation where we got a new phone number that was previously owned by someone who (must have) had awful credit, because we were constantly getting collection calls for people we didn't even know. I asked them (the owners of ULC) for advice, and they told me exactly what was told in the post... Send a Cease and Desist letter to the company. Guess what-- It worked. Phone calls stopped, end of story.
I have NEVER seen/heard any indication that they are trying to "make up" bills. I don't know the particulars of the cases posted here, but- Have you ruled out identity theft? If someone steals your info and opens an account, then the debt collectors are going to call YOU about it... Also, they only collect on the debts that they are told about, so if the original company makes a mistake, they are going to act on that mistake as well. They don't have the resources to validate every account that goes through the company.
I realize that I am preaching to the choir here, since this is a forum for people who have problems with debt collectors, but I thought I would try to give my friend's point of view on the subject...