I have problems linking my MS account to my PC account

The problem is this:

My current PoE E-Mail adress does not exist anymore, the site were it was from doesnt even exist anymore. I used that E-Mail adress in 2013 and it was there until 2021 or so I believe?

However in order to link PoE to my XBox, or better said MS, I need to follow an E-Mail sent link. So I wanted to change my old non-existing mailadress to the current one I also use for the MS account.
I cant do that because a link goes out to my currently saved E-Mail adress once again to finalize the changes - which, as I said, does not exist anymore.

I'm stuck. Please help me solving this. I wanna link before I buy into the PoE2 Early Access. Thanks in advance.

I would really appreciate help. Did I maybe post that in the wrong subforum?