Settlement made, now I'm being billed balance!

I took out a loan a few years ago and because of several unfortunate occurances in life, I fell behind in my payments. I started getting a ridiculous amount of phone calls from a collection agency a few months back. One agent went so far as to tell me that the outcome of my decision could "affect you AND everyone else in your household". They were rude, ugly and downright mean. A couple of months ago they offered me a settlement. I could pay a certain amount by a certain date, which I did. Today I get a bill from the original creditor for the balance. I haven't made any calls as yet, but because of how mean and intimidating they were in the past, I want to have the knowledge of my rights in front of me before I contact anyone. The debt was $4900. They settled for $3000. I was less than $600 behind. I paid the $3000 and am now being billed for the rest. All of the "settlement" was taken care of via the phone, so I have nothing in writing, but I know that I did not misunderstand what a settlement meant. Any advice would be greatly appreciated.

Unless you get a settlement in writing they can collect and keep trying until you pay it off and get a release.

...of course any amounts you paid must be subtracted from what you owe...keep all records

The original creditor isn't the same entity as who was calling and being rude. Those are classic collection agency tactics.

You have just been taught a hard learned lesson to NEVER deal with collection agencies and NEVER negotiate with them for any payment (by doing so you are admitting to them that the debt is actually yours when they had no real clue of that until you admitted it), and to NEVER speak with them on the phone or make any arrangements for payment.

ALL collection agencies should be dealt with in the form of a validation of debt letter, followed by a no contact letter.

You really must chalk this up to a life's lesson and pay the original creditor the remaining balance. They never did receive the money you paid the collection agency. The collection agency just made an easy 3000 off you.