Cant point my domain.

Hey guys,
I recently wanted to point my domain “chulte.de” to the infinityfree nameservers to add is as a alias domain in my client area.
One week ago i changed my nameservers at namecheap (its my domain provider) to
ns1.byet.org
ns2.byet.org
ns3.byet.org
ns4.byet.org
ns5.byet.org
and pressed submit.
One Week later I still couldnt add my domain to infinityfree, so I wrote the namecheap support. He looked into it and said my nameserver selection was reverted, cause of a missing zone plain text file at the nameservers, which is needed for every .de domain at the nameservers.
Can anyone help me with this?