I have set up vpn/stunnel.
Unfortunately NetworkManager is not handling this type of connections so until now I was connecting system to stunnel followed by vpn and at the end I had to edit resolv.conf This worked for the whole session (after system restart I had to repeat these steps again including editing resolv.conf)
Unfortunately, after one of the updates resolv.conf us getting updated after each few minutes.
My question is how can I stop (NetworkManager is disabled) rewriting resolv.conf for session?
thank you
sudo chattr +i /etc/resolv.conf
thank you calvinh for the solution.