'I came' vs. 'I went'

You're using the past to answer in the present and that's where the issue is. I would suggest that your answer should have been "I don't know, I'm at home/I'm back at home now".

If you were talking the next day however and were asked "when did Katie leave Sarah's?" you could have answered "I don't know, I'd already come/gone home", depending on your location either at home or not when having that specific conversation.

Hope that's helpful!

In general you "come here" and "go there". As "went" is the past participle of "to go" I can see your mother's point. However, in my idiolect (I'm a native British English speaker) what you said sounds completely normal to me.

I think in "go home" from work (/school etc.), the focus is on leaving work rather than arriving at home. Hence it is "go {somewhere} from work" rather than "come here {from work}".

I am also confused. A European friend texted me today and said my family went to me today. It obviously doesn’t not sound right and I corrected her by saying my family came to visit me. So I think her location is important unlike what I read above. They went to my house vs they came to my house is entirely dependent on one’s location.

It really just depends on the frame of reference that you intended at the time of your statement.

If your point is that you were not in a viable location to be able to answer the question, ie. if you want to highlight the fact not only is your present state inadequate for answering the question, but it's been that way for some time so there's no way I can answer your question in good faith...then you nailed it.

A simpler analogous method to choose which one more precisely iterates the idea you wish to convey is:

Did you picture the place your friend still thought you were?

Or did you picture or actually look around at your contemporaneous environment (inside your house) while formulating your response?

In this latter case, the second one would be the more suitable.

The question has nothing to do with grammar: the sentence does not, even arguably, violate any rule of English grammar. It also has nothing to do with truthfulness: the sentence was obviously true at the time of its utterance. The question is a matter of pragmatics.

If your mother's objection were fully developed, it would probably be that 'I went home' does not convey whether you are still on your way or have already arrived, which makes it less informative than 'I came home'. Usually, she might argue, we don't choose a less informative expression when a more informative one could be used with the same amount of effort.

In your defence, you can argue that the extra information conveyed by 'I came home' would be distracting given the overall purpose of the communication. It is irrelevant to your point whether you are home or still in transit; the only thing that matters is that you have left the place where your friend might be. The communication is focused on that place, and 'I went home' arguably fits that focus better than 'I came home'.

I replied "I don't know. I went home already."

It is the tense that is wrong. You are referring to your [lack of] knowledge about your friend. You intend to say "I don't know what happened to him, I had already gone home."

Thus "I don't know. I had already gone home [at that time]."

The past perfect is correct as it refers to a completed event in the past that gives context as to why you do not know.

go and come are about directionality and location of the speaker. It is not about grammar, it's about pragmatics.

If I am home: I say on the phone to someone.

• I've come home or I am home now.

If I am not at home: I say:

• I'm going home now.

If I am not at home and speaking to someone about go + home, I say:

• I went home at lunch time and came here afterwards.

Direction and the speaker:

If you are moving or have moved away from the place where you are, you use GO (away from it).
If you are moving or have moved to the place where you are, you use COME (to it).

And if you are at home and say went home, you are a dodo bird. Because, really, you went to work or school or the office or the store and you then came home.

In short, if I am at home and say: "I went home" to someone there or on the phone, I'm a real dodo bird.

The same is true (in formal terms) of bring and take. Now, I shall be not going into that one here but am interested to see who can guess the most misused one (bring or take), which, has now been absorbed into the American idiom so thoroughly you need a special tool to remove it. [by the way, that is a joke]

And by the way, the same is true in French, Spanish and Portuguese.

venir/aller venir(se)/ir(se) vir/ir

You would never say on the phone to a person, if you are at home: Je suis allée chez moi tôt aujourd'hui. [go] You would say: Je suis venue [ou rentrée] chez moi tôt aujourd'hui. [come]