Westlake Financial Services California Harrassment calls after cease and desist letter Los Angeles, California

I have my vehicle financed through Westlake Financial.  Collections start to on the next day after your payment is due.  I am not 10 days late as of now and receiving calls 3 times a day from a private number.  I have sent 2 certified cease and desist letters which they have on file.  I have confirmed this several times. At one point, the person who left a message stated that she saw that I had a cease and desist letter on file and to disregard the call.

I received a call from a person named "Gabriel" who was rude and lied that he was from a vehicle recovery place and that he was going to repo the vehicle.  Another person who refused to state who he is, Heavy Hispanic Accent, called and stated that my he cancelled my registration at DMV.  Another lie. 

My cease and desist letter has been on file with this company for almost a year, and they still call 3 times a day and call my references as well.  How do I stop these people.  Why don't they abide by the cease and desist letter.  Can they be sued.  I would like information if possible to start a lawsuit.  Also, they will not work with you if you need to restructure your loan or if you are going to be late due to being laid off from your job.