Ask HN: How to make Facebook forget me without access to my email?

I had a facebook acccount when I was at university (10 years ago). Haven't logged in for over 7 years at this point. I have long switched email addresses and no longer can remember my login details for that email - I doubt it still exists (as webmail accounts tend to expire and get deleted after x years or so). I have tried to recover my logins to both FB and that email without success.

I created a different facebook login through which I have repeatedly reported my dead account asking for it to be deleted, to no avail. This was expected until..

Enter GDPR. I am in the UK, I am fairly sure they have to delete my data upon request. All good, but how can I actually prove that I own the profile without my login/being able to receive emails? It's me in all the photos of course, but I doubt that's going to get my request processed..

Has anyone else been in this situation?