Harassing phone calls

I and my family have been recieving harassing phone calls from our land line by phone number 972-243-7443 and occasionally 800-732-7747 which are linked to Monitronics Security in Texas.  Before these phone calls, I have never heard of this company.  Also, I have had my phone number for many years.  They (Monitronics) have been calling several times a day for the past month, always on a week day and during working hours.  I screen all my calls so the answering machine tells them who is at the residence, yet they never leave a message... except to let the phone ring and wake our baby.  When I do pick up they ask for a "Bert" who I tell them doesn't use this phone.  I have asked them to not call this number several times, but they still keep calling.  My number is on the national "Do Not Call Registry" but this doesn't seem to deter them.  Also, through my land line phone service, I have a phone blocking feature that is ineffective for these numbers.  Further action is pending on my part if they continue to persist in their harassment.  As with any company, I would think very carefully before doing any business with these people.