Want to upgrade from Wavelab 2 to current one, but Steinberg site didn't recognize serial

You should try logging a support request in MySteinberg / MySupport, it’s worth a shot but I wouldn’t hold my breath. That’s a really old version! As you’re new here, it’s worth mentioning that this is a user-to-user forum, although Steinberg staff are sometimes active here (including the great PG himself!). Sales enquiries must be directed to Steinberg themselves.