I never answered.  They never left a message.

I didnt answer & they didnt leave message.

Did not leave message.  Must be a spam call that moves on when the caller sensed there is no human to talk to.

After a million calls I decided to answer to tell them to stop calling.

They are trying to sell some kind of online marketing service for "my business". I think they scan domain registrations online and contact the owner if the info is available. Definitely undesired and annoying solicitations. - especially when calling my mobile phone.

They did not give the company name and when I told the person to stop calling he just hung up on me.

fake,spoofed number ! calling all the time . Will report it to FTC!