"....any advice for reconnecting this line?"

Yes...and for the entire project. Hire this done. You clearly don't have the skill for this job and you've seen the consequences when something isn't right and it leaks. Suggest abandoning the guesswork you're currently engaged in. We're not there; we can't see what you're doing; and I, for one, find understanding your written descriptions difficult.

If you're trying to reuse the old ferrule and captive nut, there's only a slim chance that the threads aren't the same, but maybe the old nut is clogged with lime from a very slow leak. If you could soak it in vinegar or lime-away you could clean it off. But you can't because the nut is captive to the ferrule. So, if there was any leeway I'd cut off just below the old ferrule and clean the supply line and use the new ferrule and nut that came with the new valve. You'll probably need a new very small tubing cutter assuming you don't already have one. The new shutoff will then go on very easily.
Casey