If they block you, they can insist that any further contact is 'harassment' or violence against them. If you give in to the human impulse to reach out to them, or if they can manipulate you into blaming yourself and then you offer an apology, then they'll use that as evidence that you are disrespectful and violent.

My experience of dating narcissists is that the manipulation and gaslighting starts early. If you don't respond to it by submitting to their control, and if you try to assert your own will, they will be triggered and will respond by waiting for you to make a mistake that they can blow out of proportion and then use to tear you down. If you respond to their efforts by attempting rational communication or pointing to their own previous bad behavior, they will marshal their flying monkeys and hustle you away from them.

Because they can't tell the difference between their feelings of being triggered and emotionally attacked or violated, as opposed to the action you took, your intentions, and the current state of affairs in the moment. They're busy playing out a past trauma in which their boundaries were persistently violated, they really did experience severe emotional harm, and they had no power.

The fact that they are currently harming you in a similar way to how they were harmed in the past has escaped them.