letsencrypt delete certificate

I've a problem with my le certificate. It didn't update automatically and expired on 05-06-18. The next day I did a manual renew from with in the letsencrypt plugin. That didn't work either at the first time cause I had closed port 80. The next try gave me a success and I had a new folder in the /etc/letsencrypt folder domain.conf-0001 or similar. However in the system-certificates-ssl tab still the old, expired cert was listed. I tried again to renew and again I got a success with a new expiratian date of somwhat july (and domain.conf-0002). Still the old cert was listed in the SSL tab and I can not delete it from within the gui (greyed out).

I tried:
1. delete the old conf file
2. delete the /etc/letsencrypt folder
3. uninstall the plugin
4. reinstall the plugin
5. recreate the letsencrypt folder
6. I have read in another thread related to OMV 3 that a purge may help... didn't
7. ATM I use OMV without cert (have removed all references within the gui to it) and the same for Nextcloud, still I can't delete the old cert (as said it's grayed out)

Has someone an idea what else I can try?

Thanks,
Thomas

Only way to get rid of the delete the existing cert within the le plugin, creating a temp one for another domain but as well for the /var/www/openmediavault/ folder.
Then the old cert was gone in system-certificates-ssl and I could switch back to the original domain and create a new cert for it.