I feel stalked by the Rentenversicherung

The title is a bit exaggerated, but I'm already fed up with Rentenversicherung. As part of a process I was involved in, I asked the Rentenversicherung for a breakdown of the payments I had made. They wrote back saying that it would be several months before I could receive the document they send out every year... So far, so good.

Then they sent a letter asking for confirmation of the studies I had done in Germany, so I sent proof from the university and the German course I had taken when I moved to Germany and how long did I study. I understand why, so no problem.

Then they asked for photos of my high school diplomas from my country, etc. So I sent my high school diploma and my university diploma from my country.

Then they asked me for proof of how long I studied in my country, to see when I started university and when I graduated.

Is this normal? Why are they interested in what I did before I lived in Germany?