How to deal with unsupportive parents that are otherwise decent?

Hi all, this is going to be a long one but I hope some of you stick with me and can give some advice.

I am FTM, in my late 20s, happily married, and fully independent from my parents. I started T last year, and this summer while my parents were visiting, my mom basically asked if I was trans (apparently her family pointed out my deep voice and were questioning what was going on). I had decided not to lie to anyone if they asked me, so I told her, extremely nervously, that I was a trans man. I gave a few details about what it meant/how I knew, etc. and she seemed alright, but things went south later. She told my dad when they got home, and I was getting texts about how "the pain is so bad [they] don't want to be on this earth anymore." It was obviously not the reaction I hoped for, but I didn't expect things to go very well considering how religious they are - the type of evangelical Christians that push Jesus on you but never actually go to church, for some context.

My next step was to send a letter to them. Since their main concern was how they thought our relationship had to change, I explained how it had already changed from my perspective, and how that related to me not wanting to come out to them prior to starting T. That led to a phone call where, among other things, I was told they would never call me their son or use my new name. Very directly, no room for misinterpretation. This was incredibly disappointing and upsetting, so I took some time to go low-contact with them and consider what I actually needed from our relationship.

Well, I think I determined that I don't actually care to have a relationship with my parents. I have really only spent time with them/called them over the years since I moved out because I felt obligated to. I even asked my partner if he actually enjoyed calling his parents (his answer was yes), because I can't think of a single time where I called mine just because I wanted to. A lot of this is due to how religious they are, and how uncomfortable they make me with their reminders that I'll go to hell if I don't accept Jesus.

There are a lot of extra complications here, starting with the fact that they aren't terrible parents. I didn't have a miserable childhood, they have never been abusive in any way, and until I came out as trans, they have always been supportive of me and everything I've done. I am an only child and have been my mom's entire world from the day I was born, so I completely understand why this is a shock and very difficult to digest. I strongly encouraged them to go to therapy to work through their feelings and grief over losing their daughter, but the only thing I've heard on that front is that my mom's therapist said she never has to call me by a new name if she doesn't want to. On top of this, my own therapist suspects that my mom has a personality disorder, which complicates our relationship further. And on top of THAT, my mom and multiple other family members have lots of health issues going on that make it unclear how much time anyone has left.

It has been a few months since my first letter, and I've only talked to them on the phone a couple times, so I feel pretty guilty about essentially leaving them in the dark. I have written 2 more letters but have not sent them because I'm really at a loss here. My most recent letter, which I fully intended to send until today, pretty bluntly lays out that refusing to ever address me as their son is disrespectful and crosses a boundary for me, and I am not interested in spending time with them if they continue to cross that boundary. I think sending this might have the (secretly desired) effect of them continuing to refuse to call me their son, resulting in our relationship falling apart. But there's a part of me that doesn't think this is fair to my parents, and also worries that I will actually regret cutting off contact with them, especially if my mom dies from one of her various illnesses.

Currently I see 3 options: don't send a letter and only respond to my parents' occasional texts (stay in limbo), send my current letter and let my parents deal with it how they will (maybe end relationship), or write a new letter that gives them some more context about me being trans (maybe encourage acceptance??). This is where I'm really hoping to get an outside perspective. What would you do in this situation? Is it wrong to want to end my relationship with my parents, despite the fact that they are not abusive to me? Do I owe it to my parents to go into more detail about how I know I am trans? Would this actually help them understand me better and possibly get them to accept me?

If you made it this far, thanks, and I hope you can share your thoughts. I know there's a lot here - it's all stuff I've discussed with my therapist, but I really need the perspectives of fellow trans folks right now.

TL;DR: My parents aren't supportive of me being trans but have otherwise been decent parents my whole life. I need some advice on whether it's okay to cut contact, or whether I owe it to them to provide more details and hope they'll come around.