credit collections

What is the name of your state? wa I am dealing with a nation wide tool company that was owed money. They called and left a number to call back. I called that number and they made an offer that if I paid that day they would lower the amount owed. I paid the account in full. Now 4 months later I have a collection company calling saying that they received the bill for collection and that I owed their fees. What are my options.

was the offer made in writing? Creditors are notorious for saying "no we didn't make any offer" otherwise.