The phone numbers make no sense

So, Marla tells Narrator that he left a 'forwarding number', so THAT is how she can call him in that dilapitated house that shouldn't even have a functional phone line, but whatever.

How does that work? Whom did the Narrator think to leave the phone number of that particular house? Why would he not only do that, but even think to do that? For whom? He has no friends, his boss has no business calling him at home, but even if he (the boss) did, he (the Narrator) wouldn't give him a 'forwarding number', he would just give him the number of the house.

So where did Marla really get that number, and if 'nothing works', then why does the phone work?

Secondly, Marla calls him at workplace at the exact right department, I can't remember exactly but something about 'Complaints and Liability' or something.

So, the Narrator, who has been shown to hate Marla and try to avoid her to the point he's perfectly willing to let her DIE when he could easily rescue her, at some point in the story, gives Marla his work phone number and extension.

Huh? What? How? Who?

How can this ever happen? If you were the Narrator and you hated Marla, would you _really_ even tell her where you work, let alone give her the number? Be honest.

What kind of sense does any of this make?

Also, how would the cops also get the number of that particular house? Whom did he give his 'forwarding number', as if people call him all the time, since he has no friends or family..? The apartment manager or something? JUST IN CASE the cops or Marla happen to call..??

Wouldn't the cops rather call him at work anyway, during, you know, office hours and all that?

Not that much of this movie makes any sense whatsoever, but this is one of those things that really makes me think about how it all must have happened.. I mean, they do 'exchange phone numbers' at one point, but how does that translate into a 'forwarding number' and 'work number'? Wouldn't he just give her either his cell phone number or his home number, and that's that? Even if we can swallow the 'forwarding number' stuff, Marla should not know his work number at all.

Heck, the Narrator never even gives his NAME to her, why would he give her his fully-detailed office work number, that would basically give Marla access to all his details...? I ask you, does that make sense?