If they are a bonafide debt collector they are allowed to pull your credit report.  I'm not sure whether they can pull a hard or soft report.  However, you can certainly send them a cease comm letter, however, I think you would be better off sending them a debt validation letter.  It will legally stop them from calling and will force them to go to the original creditor to both prove that you owe the debt and that they have the legal right to collect it.  However, after the first time they talked to you or the first message they left they were required to do this:
Federal law (FDCPA) requires them to send you a letter (US MAIL ONLY) postmarked within 5 days of their first contact that contains their name, physical address, the creditor’s name, and the amount of the alleged debt.  It also must contains “mini-Miranda” telling you that it is an attempt to collect a debt and that all information will be used for those purposes.  The one other important thing that this letter must also have in it is that you have a right to dispute the debt within 30 days of receipt of the letter and if you do so, all collection activity must be stopped until the debt is verified.

It sounds as if they are making multiple violations of Federal and State Collection Laws.

You need to send them a certified, return receipt debt validation (by law they have to go back to the original creditor to prove you owe the debt) letter (think of it as the best $6.59 you ever invested).  Also send it first class mail in case no one will sign for it.  Make a notation of that fact at the bottom of the letter.  You also need to report them to the proper agencies to which I have provided links to.  Then you need to go out and get a consumer lawyer to sue them on a contingency basis (no money out of your pocket) and let them pay you for the harassment.  If everyone did these three things, these crooks would be bankrupt and we would all be the richer for it.  Use these web sites to find an attorney in your state that will probably take the case on a contingency basis (no money out of your pocket up front):  http://www.consumeradvocates.org/
http://www.consumeradvocates.org/find-an-atto ... tates_value=All

First, you should make a complaint at this Federal Agency, and while there you should also read up on how debt collection is supposed to work as well as what your rights in this matter are:  http://www.consumerfinance.gov/

Also file a complaint with your State Attorney General's office.
List of State AG’s offices:   http://800notes.com/faq/attorney-general

Are you even sure this is a real attorney?
Whenever someone tells you that they are a "lawyer", the first question you should ask is what state(s) they are registered in and their BAR number for that/those state(s).  Then go to that state and check them out, contact them directly using the information in the state registration, as these crooks have been known to research real law firm names and attorney names and impersonate them.