It was important enough to be included in Isaiah, and important enough for you to cite earlier - but now you say it’s not important? That’s a Mandy Rice-Davies moment for sure.
So? Isaiah doesn’t say that his mother will use those names. Isaiah does say that his mother will call him “Immanuel”. Do you have any reason to think Mary ever called Jesus “Immanuel” other than that is what the prophecy said he would be called? Yes or no.
The best translation is “and shall call his name Immanuel”. It is not clear this his her calling but it may be. Whether she used this name or not isn’t relevant. What is relevant is this name describes the essence of Jesus.
Be careful not to cherry pick. The bible has redundancy which helps with language ambiguity.
Jesus is a man. Christ is a title. One can expect Christ to come, but not believe it is Jesus.
If the prophecy says she “shall call his name Immanuel” then whether she called him “Immanuel” is relevant.
I’m not the one trying to ignore inconvenient verses.
Why is it relevant given the overall context?
This is a silly squabble.
It has nothing to do with what Mary called him.
She might have called him ‘Josh’. 
Right, @swamidass?
Did you quote the wrong verse deliberately or accidentally?
But Muslims expect the man, Jesus, to come back.
It’s the big picture.
And I’m sure she did recognize who he was and in effect call him Emmanuel, just as Christians do today.
And you’re “sure” because…?
Let me see if we have this straight:
In the Jewish tradition as recounted in the OT, there was a belief that there would someday come a Messiah, and this person would be referred to as “Immanuel.”
Then Jesus came along and led a group of Jewish followers. Some of them came to believe he was this Messiah, and started calling him “Immanuel.”
Is this what you are calling a fulfilled prophecy?
That isn’t it. Try again :).
Christians don’t call Jesus the name immanuel, but we think he fills that prophecy. Why?
What does the Name mean?
That’s the big question. From what I can see, the Messiah is described as both a spiritual AND political figure. Jesus seemed to fall very short on the political side. The Messiah was supposed to be a king or a ruler that ruled over lands and kept the Jewish community safe in their homeland. These events were supposed to happen while the Messiah was alive on Earth (i.e. in his time). Jesus didn’t do that. So can the Messiah fulfill some of the requirements, but leave a large portion of other requirements unfulfilled?
The name literally means “God with Us”, and this is literally what Christians believe in the doctrine of the incarnation. Immanuel is a statement of the incarnation.
Now at the time of Isaiah, some scholars wonder Isaiah 9:6 refers to an actual child born at that time actually named Immanuel. This follows a common pattern in the old testament of circular or repeated typology and fullfillement of prophecy. The first fullfillement was proximate and literally a child named Immanuel. This kid showed God had not forgotten them in that moment, but this kid didn’t fill most of the prophecy. The complete fullfillement was later in Jesus and literally God in human form, God with us.
Since we are talking about Jesus being God, we are talking about the government, the governing, of the universe, and the immaterial ‘universe’, as well. So, yeah, the government is upon his shoulders. Just because you don’t like his governing and his judgment, and consider that reason to reject him… well, that’s another issue.
That’s not what was described in the prophecies.
Prophecy is both figurative and literal. Much of it is written in poetic form, which lets us know that we should expect some metaphors.