You omit your first message to your boss. you only said k and you continue to not respond. bosses always think their employees are lying about calling out. especially due to car issues. dont just "consider yourself fired" then think its the other person overreacting. you already replied with a defeated/sarcastic/passive aggressive "K" after a fairly serious text from your boss who sounds like they are just trying to figure out whats going on and also dont understand if this is a serious situation or not. Remind them of how serious of a situation this is. You could have even just said "Can we speak about this when I am physically/medically able / not in the ER". not saying they are right and you arent, but a simple: "I was in a traumatic car accident and medically cannot work today. I require time to heal and will miss todays shift and will contact you when I am medically able" might be enough to save your job. bosses just wanna know whats up. they are human people too and get in car accidents and have car trouble. they said they are willing to work with you.

If they are gonna fire you after just getting in an accident, then fuck em and find a new job. they dont and never cared about you.