DNS Problems after ProtonVPN usage

[wahl.s]

Hi all, I searched pretty long on this topic but couldn't find the right solution for my problem, although I discovered many people seem to have issues with the DNS.

I installed ProtonVPN (using Snap) on my Dell laptop (Zorin OS 16 Core) and everything worked pretty fine. On one point I disconnected the VPN and tried to browse the internet again without it and I couldn't load websites anymore. I tried Firefox, Chrome, Brave and Opera but nothing. But I discovered that if I connect to the Tor-Network it's possible to browse the internet and load websites as usual. Tried to reboot and switched of the modem several times but didn't work. I can't do anything for what I need an internet connection except browsing via Tor. The Wifi works as I am connected with several other devices without problems.

Any ideas what the problem might be?

Thank you for your help!

[wahl.s]

Thank you for your reply! This really helped me! I didn't enable the killswitch as I only use the free version but it seems that there was a VPN connection still running in the background.

I identified the VPN connection using the command:
nmcli connection show --active
Looked for any connections that begin with prefix pvpn- This usually includes pvpn-killswitch and pvpn-ipv6leak-protection, and may include pvpn-routed-killswitch. Deleted all these connections using the following command:

nmcli connection delete [connection name]