Ifdown & ifup are not working

It is legacy, and can conflict with the new method that RedHat provides: network manager.
Get used to the nmcli command!
man nmcli
And maybe some tutorials.
For an interactive use there is nmtui

I think the corresponding commands are

nmcli dev disconnect eth0
nmcli dev connect eth0

nmcli dev show lists the interfaces.
Usually you work with the connections:
nmcli con show
You can down (and up) a connection, but type auto might bring it automatically up.