Where would I find that? Phone can make and receive calls, texts etc.

https://eu.community.samsung.com/t5/other-smartphones/my-phone-number-unknown/td-p/226777/page/4 

believe it or not, this is what I had to do on my S21 ... put it in my iPhone SE and put it back!

Settings, About Phone.

Are you saying that

 

1. when you call somebody, on their side it shows as unknown number?
2. or when you check the device info, it shows "Unknown"

For 1, open the phone app, go to Settings & look for "Caller ID"

For 2, if you are talking about Settings > About this phone > Status, then I don't know. Some phones always show my number, others have never displayed the SIM number.

Ah, so it was #2. Guess I'll keep an eye on this thread.

Follow link above it works.

Except I dont have an iPhone.

OK, I was trying to set up Chat in Google Messages and it couldnt verify the number so I thought that was the problem.

Yes, its a ported number. Oh well, will keep trying to figure why I cant get Chat setup, thanks.

I find it's SIM (and possibly carrier?) dependant but generally doesn't make a difference to functionality. My current main SIM originally had a different number before I ported my main number to it yet it still shows the correct ported number in About. I have a dual SIM phone swapping to different carriers at various times (including porting my main SIM every year or so) and whether it shows a number at all, whether it shows the correct number (when porting is involve) always seem to vary for me. I have had a few SIMs which shows nothing or the original (pre-port) number. All very strange but it's always worked out for me. YMMV.

OK, so I guess thats not the reason why I cannot get Chat Features set up in Google Messenger. When I try, after putting in country code and phone number (021 xxx-xxx) and hitting Verify Your Number it just says Trying to Verify Your Number and nothing further happens, never get the code from Google.