After the uninstallation, have you tried to run the removal utility for your older AV? Remnants create conflicts too, so get rid of them. Please use Windows Safe Mode to run it.
Then delete the firewall rules related to avast. Reboot, and avast will try to connect. The firewall, in "learning mode" or equivalent, should ask you for permission and so you can rebuild the correct updated rules again.
After the "fix" or repair of avast, you need to reboot before retesting the results.
Please report back, so we can give you additional instructions if necessary.