THAT WAS IT!! Thank you so much! You were right that the Cordial cable has had a little plastic bag with 2 screws in there. I was thinking that the screws are the same as on the connector and they are just spares. But changing the screws by opening the connector and replacing with the ones in the plastic bag NOW makes it possible to tighten the connector to the plug.
Consider this case as closed now 🙂