This is an issue I've had in the past. He's a controlling, emotionally abusive man who I speak to as little as is possible. At workplaces in the past, even though I don't tell him where I am working, he will go out of his way to find their number online and jump through the hoops to speak to someone at the company. Then he starts on a sob story about how he needs to speak to me and I'm just not answering him.
Unfortunately the past two times this has happened, everyone thinks it's a huge joke and tells me stuff like "you should always call your father! Don't ignore your dad!" and it's like uhm... there's a reason why I am and there's a reason why he's calling (to undermine me at work).
I'm currently self-employed so this isn't an issue, but I'm planning to go back into the workplace and the idea of him doing this to me is very stressful. He basically tries to weaponise my workplace against me and people fall for it.
Tell HR at the new job that a stalker who claims to be your father will eventually be reaching out, and do not let him through.
Some have had luck with getting family stalkers to go away by sending a certified letter formally demanding no contact by any means, and/or through any third parties - which you can give to the authorities to prove you formally asked him to stop contacting you. Document and stay safe.
Sorry you're going through this. I had the same thing with my mother. I proactively told my manager that my mother was "unsafe" with zero context, and if somebody with her name or claiming to be my mother called, do not confirm that I work there and if she shows up, call the police immediately. I was really scared to ask them to do this but they were all very supportive.
Can you get a restraining order? They can include the person not being allowed to go to or contact you at your workplace.
Sorry this is happening to you.
Domestic violence is workplace violence because it's always in danger of spilling into the workplace. The workplace has the responsibility to protect staff, customers, etc from workplace violence.
It needs to be brought up asap with new jobs just as a disclaimer. "I'm a victim of a domestic violence situation and want to give you some information related to the perpetrator(s) so staff are educated on how to prevent a possible incident." If you had a restraining order against the person I'd provide that as well. I wouldn't disclose until I already work there and claim it's a recent development. If something happens to you or anyone else at work because of this your workplace is liable. The only way to get a business to take anything seriously is to make them aware of their legal obligations.
i suppose you could accept the call, say nothing and hang up. sort of a grey-rock tactic.