Can't place WhatsApp calls as I'm told my phone number is no longer registered
In the message:

Can't place call because this number is no longer registered on WhatsApp

the word &quot;this&quot; means &quot;the number you're trying to call&quot;, not &quot;your own number&quot;.
Calling other numbers will work.
A belated thanks goes to @aBochur for drawing my attention in this direction.