You are all free to call Mason anything you want.
You can choose to honor his wish to be referred to as his chosen gender, or you can ignore his wishes completely, choose the dark route, perpetuate his abuse, and mislabel him for your own comfort.
That is entirely your choice.
Outside the novel you can also choose to call him what you like too.
If it makes you more comfortable labeling Mason something other than how he sees himself, you have that ability.
Along those same lines, should you make the choice to ignore someone's gender, simply because it makes you feel better, and for some reason you won't respect someone else's wishes, then it might help you understand if you experienced it from the other side.
So, from now on I'll call you jack. You may have given yourself some other distinction, how you wanted to be addressed and seen in social interactions, but that doesn't matter. You look like a jack to me, regardless of what you might choose or prefer, so I'll call you jack.
If it bothers you, remember that you've already stated that how you see someone is more important than how they see themselves.
Which means you're just going to accept it, right? That's what you expect others to do, so it should be okay for you too.
I mean, you could argue or disagree, but you wouldn't want to cause any drama.
Looking forward to chapter 10, the continuation of character storylines, progressing into the next big phase of the story, and seeing how we can help Guy handle everything that's thrown at him.
Have a good one.