Hello.
I had this only when I recently ported my number to another UK carrier / network and it still showed the temporary sim number in About Device and also on the Samsung Kies programme on my computer.
My factory unlocked international Samsung had previously been on the last few months of oanother carrier plan, where it showed the number as Unknown.
I had a store replace my new sim and it again shows as Unknown on the new network.
Have you had a new sim. You can have it changed. It's highly unlikely people you call will see the wrong number, but you probably have checked that.
Sorry I can't be of more help.
Down to your carrier I think.
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