I am not sure when I got introduced to NVC the first time, it's been some years. I really dig the concept and think there should be no other way ever being communicated with/in.
However, even if you think you are doing it, are you actually doing it correctly? Like following NVC actually requires you to dig deeper. So either you are crystal clear in every moment and so mindful that you always know what's going on, or you might actually need to take a step back, pause and think/feel what is going on.
Like it's not just about, so here is your behavior, this makes me feel sad, would be great if you can do that the next time.
Ok, if you're doing that, that's already a good start.
But..why should the person do that? What is your need?
Sure, if someone attacks you, you can say "well me need is not to be attacked". Guess more likely it is to be respected, to be seen, to feel connected and valued.
This is from the perspective of an argument or someone externally involved. You however can also use NVC for yourself when no one else is involved. More often than not, it's usually not about the others, but only about you.
Here's a quick video which goes through this quite nicely within 5min. I would encourage you to listen to it and then 2-3 times a day, just go through the motion. It's not about being another chore or todo list item. Rather, do it, hopefully it feels good and comes naturally. Don't beat yourself up too much, if you don't follow through. Sometimes it's just not the right time.
Anyway, here is the video.