It sounds to me like this agency might have violated multiple rights of yours.
Feel free to contact my office on Monday, or sometime early next week. We can try to put you in touch with an attorney who can assist you in your area. In my opinion, not legal advice, you are entitled to max $1000.00 under the Fair Debt Collection Practices Act (FDCPA). This company should not get away with such misleading communications.
Please do not take my answer to be legal advice that would establish any attorney-client relationship. Please take it as a general response from my own experience in response to your question. I hope you find it helpful.
Lucky for you, the best consumer/debt collection attorney in the West is right around the corner. Contact Karen Oakes. She is dead-on accurate regarding your rights and she cuts creditors who violate the law no slack. You'll find her in the phone book.
This answer is offered as a public service for general information only and may not be relied upon as legal advice.
The collection agency should be able to provide an answer to your SOL question. I think KS law is most likely to apply.
They should not call you after receiving a C&D letter. If you want zero collection letters then tell them in writing that you dispute and never intend to pay. If they still want to collect after that then they would pursue legal action (in small claims court).
If they continue to bother you, you should seek a consult with a consumer law attorney. The Oregon state bar can help you find one.