Hi @teneco,
Ok, lets see if we can fix it.
Login as root and execute below commands:
First, backup… just in case 
cd
tar zcvf backup_etc_letsencrypt-2017-Oct-10.tar.gz /etc/letsencrypt/
Now, we will reorganize your certs.
rm -f /etc/letsencrypt/archive/mail.cloud-vngl.de/*
mv /etc/letsencrypt/archive/mail.cloud-vngl.de-0001/* /etc/letsencrypt/archive/mail.cloud-vngl.de/
rm -rf /etc/letsencrypt/archive/mail.cloud-vngl.de-0001/
cd /etc/letsencrypt/live/mail.cloud-vngl.de/
rm *.pem
ln -s ../../archive/mail.cloud-vngl.de/cert1.pem cert.pem
ln -s ../../archive/mail.cloud-vngl.de/chain1.pem chain.pem
ln -s ../../archive/mail.cloud-vngl.de/fullchain1.pem fullchain.pem
ln -s ../../archive/mail.cloud-vngl.de/privkey1.pem privkey.pem
And now try to renew the cert:
certbot renew
If the cert has been renewed, reload Apache:
service apache2 reload
I hope this helps.
Edit: Added rm *.pem to command list to avoid errors when issuing ln commands.
Cheers,
sahsanu