Wrong holiday calendar keeps reappearing
I have set my iPhone to the german region. But the calendar app is still showing the US-holidays calendar. If I switch the region, force quit the calendar app, and then switch back to the german region, the german holidays are shown in the app. But in system Settings -> Calendar -> Accounts -> Fetch New Data, it still shows the entry for US Holidays and after a while, the US holidays reappear in the calendar app. I contacted the support and we tried to reset my iPhone from a backup, but it did not solve this problem. Can anyone help me with this issue?
iPhone XS, iOS 16