misplaced serial number after purchase, cannot register

Hello everyone!
I need help, tried to contact support on the website but could not find a place to open support ticket.
Bought Cubase Artist 7 from an official Steinberg reseller on ebay. Did not get to install the product for a while. When installing it, it turned out that I need a serial number that was long thrown away with the box and packaging. However, USB key and disk is present. It has never been registered. I am trying to register the softwared but I can’t do it without the serial.
Does anyone know how to get the lost serial number for the product that has the e-licenser key and has never been registered. I have the original payment notification from paypal for the purchase. It was bought in Jan 2014 from an authorized dealer on ebay. It came in a sealed box, but paperwork with the serial were thrown away.

Any help would be appreciated!

As far as I am aware that serial/activation number is critical to licensing the program. I don’t think it can be replaced. I hope I am incorrect but I don’t think so. The USB dongle needs that number to add to its memory.