How can someone get my phone number from my instagram?

I have been threatened via whatsapp regarding an instagram comment.


I was threatened ("you will regret your comment for the rest of your life" kind of threat) by a phone number from a country code different from where I reside. I blocked the phone number which came from a country with +44 code.
My Instagram account is private.

​

blocked can code instagram kind life phone phone number privacy rest threat whatsapp