The people in the Softbank shop cannot help you find a number you called two months ago, not if you need it today. They might think they can when you first ask. They might ask you to wait while they check into it. You might wait for forty minutes. They might make some calls. Then they will find out that they cannot help you, that you will have to wait for it to be mailed. They will apologise and you will leave.
And it serves you right anyway. You should have registered that number when you first got it, dumbo.