Help ! I can't upgrade to 8.5

I am in a very difficult situation and I don’t know whta to do .

I have cubase 4 and i want to upgrade to 8.5 pro.
I bought Cubase 4 from Millenium music years ago when it first came out and they installed it for me and got it working with my hardware etc etc . I have an e key and it all works fine.

BUT

They must have registered it for me under God knows which old inaccessible email and who knows whta username and now I can’t access my steinberg account because I wasn’t even aware I had one !

How am I going to update my e key without any info ?
I bought cubase 4 as a boxed product not a download and I am completely stuck .

I have a new studio computer raring to go and I don’t know how to get past this.

Please,please can anyone help .

This matter has been resolved by support but I would just like to say a massive thank you to everyone on the forum for their advice and support.
As with every other post I make you have literally been of no help whatsoever .