This is a very expensive faucet-- with almost TOO MUCH STUFF trying to get thru the retaining nut under the sink! The person installing this faucet likely had a 'nightmare' getting all the pipes thru that little hole, and getting the nut and washer to fasten to something solidly!
Have you looked up under the sink, to see what it will take to tighten the large nut around that main faucet body?
Likely your sink restricts contact with normal slip joint pliers, and most Basin wrenches are not big enough to get around that large retaining nut.-- Thus the problems since this faucet was first installed!

So-- Your goal is to get the nut to tighten solidly, and prevent the stationary body from rotating when you try to swing the spout.

NOW-- If the spout has 'frozen' in the vertical tube inside the pivot point, then this has to be dismantled first. Do you have a good parts supply nearby?
Because you might need some 'order only' parts to make this repair--

I suggest you take the make and model numbers (that you supplied us)-- and go to the hardware/plumbing section of the plumbing and faucet supply store you trust-- One that can open a book to a nice big parts blow up of this faucet-- tell him your problem,and see what parts he suggests they order for you-- When they come in, then your work begins!
The parts guy should be able to help you get the right wrench, to tighten this faucet up in that tight spot, too!

May your back be strong, as you work upside down in cramped quarters for a good long day! :-)

Let us know if we can help more-

Mack B