Constant harassing for ex employee

This company constantly calls me although I have asked them on numerous occasions to remove my cell phone number from their records. A lady who worked for me 3 years ago gave my cell phone number as her second contact number. No matter how many times I inform this company they call again. I provided them with the numbers I had. I have asked to remove my home number snd personal cell phone number from their system. Sometimes they do not call for a few weeks and then they call again. I do not know how to get them to remove my number. They are wasting my time and theirs to constantly phone for an employee who left 3 years ago.