How can I find of Beitragsnummer for the Radio tax?

I’ve changed my address as of today(anmeldung) and I want to change my Radio tax adress. Previously my roommate paid it and I was attached to him. To change it I need the Beitragsnummer , but I can’t find it. I’ve looked on all my papers from Rundfunkbeitrag and to my surprise there isn’t a Beitragsnummer on my papers for some reason(example : https://imgur.com/a/aDxeYAh ). I honestly don’t remember what I did with the right paper when I did my first registration. All I have are 2 papers, both with only the Aktenzeichen number . What should I do?

by magma6