Advise on a NCO collection of old debt

For the past two month NCO has tried to contact me on my cell and I would never answer. Two weeks ago I received a letter from an attorney asking to be paid in full for an old credit card account that i had on behalf of NCO. This account is over 7 years old and I know the SOL has expired. I sent a letter to the attorney stating this fact and asking for proof of the debt. I have credit watch on my credit reports and received a notification that an inquiry had been made and guess!! who it was "the attorney"; I then proceeded to receive a phone call on my cell and at my home. I know the atty received my letter but they continued to call. Here is where I think I made a mistake I called them back to see why they continued to call me a lady answered the phone and I asked her why they continued to call me she said to make arrangements to collect the debt. I told her that I had sent a letter disputing the debt. She then stated that NCO said they would take 40% of the amount I told her that I didn't have the money but I could probaby pay a certain amount. She said she would have to contact NCO and get back with me. I want to send another letter asking for validation of debt but did I make a mistake and reset the SOL since I told her i could try to make a pymt in a couple of weeks. Sorry this is so long this is my first time doing something like this :P Any advice would be appreciated.