How could people say "Aliens have most advanced technology than Humans " while we didn't even know where they are ,how they look like ?

Exactly
They could be Microbes after all
And if they were at all intelligent they would probably have an extremely long way to come, just to be nosey, or try our Pies
With a bit of luck they will bring some Ganga

You're mixing up aliens and aliens here (and hindusufi is mixing in another set of aliens). See where incautios use of language can get you?

Aliens(a), which your "people say" refer to are non-human beings that visit Earth. Since humanity is so far (depending on your level of conspiracy theory) unable to reach other stars, their technology is by definition more advanced than ours.
Aliens(b), which you are implying, are non-terrestrial organisms of any evolutionary state living on other planets. You're right, we don't even know yet if they're out there, but it would be an amazing coincidence if they're not.
Aliens(c) in Hindusufi's sense are simply human beings with another country's citizenship.

Where I live all the aliens are human, mostly from Mexico, though we've got one Canadian.

Because unless they evolved in space, there's no other way they could reach us.

If aliens come to visit earth, they would have to have technology much more advanced than us to get here. We are not even close to being able to make an interstellar trip.

Aliens on their own planet might not have technology at all. They might be animals. They might be just microbes. We don't know.

The only people I’ve heard say that and actually be serious are in a questionable state mentally. People who believe in cognizant creatures with culture and technology on other planets are really confused and in need of some evaluations,