The reaon why the collectors are so rude is because they already have the money and they are already getting paid. Another thing is to them you are a "debtor" not a customer, not a client. Bill collections is NOT customer service. Their job is to collect the debt and that is it, not to be anyones friend because no one will use them as a customer.
Meaning if you had bad service at a resturant and the server was rude, then the restuarant just lost money as you becomming a potential client.
Hope that helps!