Cubase 5 to Cubase 10.5

I want to upgrade Cubase 5 to Cubase 10.5
When I try Register eLicenser, I get an error (This eLicenser number has already been registered by another user.)
My Cubase is activated and I don’t remember the old mail.
I need to remove activation from old mail, because I can not upgrade to 10.5
I have all the USB and the box
What should I do?