Inherited old domain with login information lost, can't verify DNS entry


I “inherited” an old Cloudflare configuration, which is registered at my Hoster.
Unfortunately all security related information, especially log-in to the “old” Cloudflare account is lost. Tried to create a new account, so I am able to manage the DNS records myself.
The transition page now asks me to enter the new cloudflare NS-Entries in my Zone file, which I don’t have access to. The Zone-file of my hoster is updated, but apparently not used for DNS-Lookups, so I’m in kind of a deadlock. Asking the support of my hoster, they point me to Cloudflare. Any usefull hints how to unlock the situation?