No DNS resolution

Okay this seem it was MY Problem!
i can't believe it. Sorry for that.

root@mvps-vm1:~ # cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.0.1
root@mvps-vm1:~ # pihole updatePihole
  [i] Checking for updates...
  [i] Pi-hole Core:     up to date
  [i] Web Interface:    up to date
  [i] FTL:              up to date

  [?] Everything is up to date!
root@mvps-vm1:~ # pihole updateGravity
  [i] Pi-hole blocking is enabled
  [i] Neutrino emissions detected...
  [?] Pulling blocklist source list into range

  [i] Target: raw.githubusercontent.com (hosts)
  [?] Status: Retrieval successful

  [i] Target: mirror1.malwaredomains.com (justdomains)
  [?] Status: No changes detected

  [i] Target: sysctl.org (hosts)
  [?] Status: No changes detected

  [i] Target: zeustracker.abuse.ch (blocklist.php?download=domainblocklist)
  [?] Status: No changes detected

  [i] Target: s3.amazonaws.com (simple_tracking.txt)
  [?] Status: No changes detected

  [i] Target: s3.amazonaws.com (simple_ad.txt)
  [?] Status: No changes detected

  [i] Target: hosts-file.net (ad_servers.txt)
  [?] Status: No changes detected

  [i] Target: github.com (spy.txt)
  [?] Status: Retrieval successful

  [i] Target: localhost (adblock.hosts)
  [?] Status: Retrieval successful
  [i] Received empty file: using previously cached list

  [i] Target: raw.githubusercontent.com (anti-adblock-killer-filters.txt)
  [?] Status: Retrieval successful
  [i] Format: Adblockcomm: file 1 is not in sorted order
  [?] Format: Adblock

  [i] Target: raw.githubusercontent.com (trackers.txt)
  [?] Status: Retrieval successful

  [?] Consolidating blocklists
  [?] Extracting domains from blocklists
  [i] Number of domains being pulled in by gravity: 174629
  [?] Removing duplicate domains
  [i] Number of unique domains trapped in the Event Horizon: 150545
  [i] Number of whitelisted domains: 10
  [i] Number of blacklisted domains: 4
  [i] Number of regex filters: 1
  [?] Parsing domains into hosts format
  [?] Cleaning up stray matter

  [?] Force-reloading DNS service
  [?] DNS service is running
  [?] Pi-hole blocking is Enabled
root@mvps-vm1:~ # pihole restartdns
  [?] Restarting DNS service
root@mvps-vm1:~ # apt update && apt upgrade
OK:1 http://deb.debian.org/debian stretch-updates InRelease
OK:2 http://security.debian.org/debian-security stretch/updates InRelease
Ign:3 http://deb.debian.org/debian stable InRelease
OK:4 http://deb.debian.org/debian stable Release
Paketlisten werden gelesen... Fertig
Abhängigkeitsbaum wird aufgebaut.
Statusinformationen werden eingelesen.... Fertig
Alle Pakete sind aktuell.
Paketlisten werden gelesen... Fertig
Abhängigkeitsbaum wird aufgebaut.
Statusinformationen werden eingelesen.... Fertig
Paketaktualisierung (Upgrade) wird berechnet... Fertig
0 aktualisiert, 0 neu installiert, 0 zu entfernen und 0 nicht aktualisiert.
root@mvps-vm1:~ # iptables -L --line-numbers -n
Chain INPUT (policy ACCEPT)
num  target     prot opt source               destination
1    ACCEPT     udp  --  127.0.0.1            0.0.0.0/0            udp dpt:53
2    ACCEPT     tcp  --  127.0.0.1            0.0.0.0/0            tcp dpt:53
3    [DOMAIN 1]  all  --  0.0.0.0/0            0.0.0.0/0
[...]
22   DROP       udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:53
23   DROP       tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:53
24   DROP       udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:161
25   DROP       udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:162
26   DROP       tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:5666

thanks for your help