I have 2 contacts on my Xperia X which won’t delete. I’ve tried your method of adding a contact but when I try any method (from the Apps->People->Delete all contacts or from the People app and selecting them all) they’re still there. I’ve removed the SIM card and disabled the Nextcloud account, rebooted several times but still they’re there.
As one of very little patience, this is really p*ssing me off!
I’m tempted to try hacking the sql database in an effort to remove them from there.