Portfolio Recovery Cavalry, NCO They say I owe a debt from 11 + years ago...constant calls...help Norfolk, Virginia

Portfolio Recovery has been calling me for the past 4 months.  I answered the initial call, refused to give them my SSN.  They say that I have debts to Capital One and some utility company from 2000!!  I told them that I couldn't believe that they are trying to collect after 11 plus years.  They gave me a city and state where the debt was from and I never lived there in 2000.

I then explained to them that in December 2010, I had paid off every debt that I had, which is absolutely true.  I explained that we (husband and I) had hired an attorney to find all of my debts (debt from my previous marriage...ugh) and that we paid every single debt that was on all of my credit reports in December 2010, so I found it hard to believe that I owed anything to the people that they stated I did.  I also found it funny because I had just received a new credit card from Capital One!!  I said "why would they give me a card if I owed them money?"  They said that they purchased the debt from someone else.

They then told me that I could write a letter to them stating that I didn't owe the debt and "they" would determine if I really owed or not.  I sent the letter, but they are still calling 2-3 times per day.

My husband did pay all of my debts off for me (he is such a great guy!!) because he wanted me to have great credit again and to finally move on with my life.  We also have three very small children and he wants to make sure that I have great credit if anything ever happens to him. He has excellent credit and wants the same for me.

Anyway, the debts that they say I owe are in the state of Missouri and are over 11 years old.  I don't think that I owe anything at all.  Plus, it is well beyond the Statute of Limitations, right?

What can I do now?  Anything?  I am sick of the calls and I have no debt now and I do not owe the ones that they claim that I do.