When atheists ask (or repeat what they heard, they can't think for them selves): ( the question is in the picture)
The answer is quite easy.

Suppose that you started doubting being your parent's biological offspring, you wouldn't knock on every married couple's house taking DNA samples (what Atheists propose).
The first thing that you would do, is confront your own parents. Or in our case, religion.

If they turn out to be your actual biological parents through whatever verification method you chose to use, then it also wouldn't make sense for you to keep looking.
The same thing with religion, if islam turns out to be right after a serious research then why keep looking?

And if your doubt checks out, then you need to narrow down your search, again, knocking on every couple asking for DNA samples is stupid.
Through your race, age, adoption center data and other elements you can narrow down the search to a reasonable sample.

And that's how you narrow down 4000+ religions, through asking the right philosophical questions, like does polytheism make sense more than monotheism? and so on.
After that you can look into the reasonable number of religions to find the right one.

Saying that there are 4000+ religions but I don't believe in any of them is a fallacy.
Please stop repeating questions that you never attempted to find an answer to.

The Second point that I would like to address is the "you grew up in a Muslim Family, that's the only reason why you are a Muslim"
This objection can be worded in different ways but in it will always be a genetic fallacy.

Instead of addressing the Religion in itself, Atheists who use this argument rely on the effects of culture and family on the Theist and how if he happened to be born in a family that has another religion, the likelihood of the theist adopting another faith is pretty high.

This can be replied to by a couple of points:
1- Truth isn't restrained by time, geographical location, traditions or the amount of wrong answers.
2- Atheists are a living example of how a person can grow up in a religious family and still manage to abandon his faith for another.

3- I speak on behalf of Muslims and Islam when I say that Islam forbade imitation and blind following.

Qur'an 2:171-172, 5:104 and many other verses that describe how people turned away from the truth using their parents and ancestor's traditions as excuses.

Qur'an also invited us to ponder an think about the creation and life in many verses.

4- Atheism is also an ideology that is also bound by factors like geographical location. this might sound like a Tu quoque fallacy but we tackled the argument head on in points 1, 2 and 3.

Since Atheists are using the geographical location as a factor that limits the choice of a religion, why stop there, let's use time for example: if you grew up in 12th century Russia, or whatever location from that era, you probably wouldn't an Atheist.
There are other factors.

Using such arguments can only show how intellectually broke you are because you can't tackle the religion that you are arguing against head on, and it is extremely lazy and arrogant to assume that it will work on every theist you encounter.
adiós