You were on to something with the phone number.
I created an Open AI account in November and my $18 credits expired on March 1st. So, like many of you here, I tried creating a new account with a different email address, but same number. They gave me $0 credits.
I tried now with a different phone number and email. This time I got $5 credits.
They’ve gotten stingy! Who lets credits expire without a way to request more? And $18 to $5 is a big drop.