Thanks. I will have more suggestions but for now please do the following.
Open the Terminal app — it's in your Mac's Utilities folder and looks like this

At the prompt, type (or copy/paste)
cat /etc/hosts
... followed by the Return or Enter key.
Copy the results of that command, and post them in a reply. A typical example of the Hosts file contents looks like this:
##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting. Do not change this entry.
##
127.0.0.1 localhost
255.255.255.255 broadcasthost
::1 localhost
fe80::1%lo0 localhost
This is just a typical example. Yours may not look exactly like it. It may reveal a clue, or not.