You have to register yourself with the city you live in. Primarily your address, but they also ask you stuff like religion and marital status.

If you're a member of certain religions, church contributions get deducted from your paycheck automatically with your taxes, social security, etc.. If you want to stop contributing, you have to file paperwork to formally leave the church. If you're baptized, you're considered a member of the church until you file that paperwork.

I didn't know all that when I moved here and just checked the "No religion" box.

Now it's been 10 years, and I live in constant fear that I might someday have to prove I'm not a member of the church. There have been cases of churches going after foreigners for "fraudulently" claiming not to be members of the church after finding out they were baptized in their home countries.

If I file the paperwork now to "leave" the church, I'd be admitting that I was in the church and would owe thousands of euros.