Vehicle Service Department Endless notices to purchase extended service warranty Dallas Texas

Over the last 3-4 years I have received countless phone call and paper notices in the mail from this company.  I've told them to take me off their do not call list to no avail.

I also continue to get the notices in the mail.  They keep telling me my factory warranty has expired and practically demand that I purchase their extended warranty. 

The only phone number they have for me is my work number.  It's very embarrassing knowing that everyone in the office can hear my conversation with them.  I've screamed at them.  I've hung up on them.  I've told them I no longer own the car.  I've politely told them I'm not interested.  I've politely asked to be taken off their Do Not Call list.  All to no avail.