Harassed at work and jeopardising my job

I am being harassed from 6am in the morning by MBD and if I don’t answer they call my place of work. They are also jeopardising my place of work because they stating what it is for, which is completely unacceptable. Our office manager repeatedly asks them to call my cellphone and to remove their number off their system but they do not listen. I pay every month without fail and yet still get harassed. They have no respect at all. How do I get them to stop calling my work