Messerli & Kramer Law Firm They keep contacting me about a debt I do not owe and it goes back before 1999 Plymouth, Minnesota

I received a threatening letter from Messerli & Kramer back in 2006 regarding a debt I supposedly owed gong back to pre-1999.  This was not my debt, but my husband's who passed away in 1999.  I called their office and explained this.  They then filed a suit against me and that is the last I heard of this, even thought this was past the 6 yr. perscription period.  My husband, prior to our marriage, and due to the fact that we were both married before, filed a marriage contract stating all debts were to remain separate and apart from one another prior to our marriage.  I tried explaining this to Messerli & Kramer but they won't listen.  Also, as a third party collection agency, even though a law firm, they are a third-party collection agency, they have been told on numerous occasions not to call my home but they continue to do so.  The last call received was last night and again they were told to leave me alone as well as the reason I am disputing this debt and have been disputing it all along.  I was told that they would not get into the "law" with me, but I said that was fine I didn't need them to, I know the law (I'm a paralegal).  I think Messerli & Kramer need to have their "wings" clipped for unfair practices.  Although they are a law firm, they are in this case a collection agency and must abide by those rules of law.