It’s true that doctors focus on the medical side, but maybe that’s actually where something has to be changed. We’re going more and more into a multidisciplinary approach when it’s about health or mental health, but there’s still a lot of work to do on this matter and a lot of awareness to bring. BMI, considered alone, doesn’t really mean anything. What is treated is not only symptoms, but people. With their physical health, their mental health, their family situation, their employment situation, their personal story, their genetics… All of this impact our health and our capacity to access to healthcare. And receiving this kind of email that you (@Danilovenj) mentioned can push people to stop going to their doctor or receive the healthcare they need, unfortunately. As you said, this doctor has your medical history and has been informed about your struggle. So whether they did a mistake, or they don’t understand what eating disorders are truly.
It always makes me sad to realize how much eating disorders are misunderstood by some doctors - if not ignored - because it’s something I’ve been struggling with for more than a decade now, going back and forth in recovery, and I understand how isolating and destructive it is to struggle with that.
Short story: I tried to talk about it once, with a doctor. I was young and totally afraid to reach out - like the very first time I do it. I finally managed to talk, and the doctor told me I should try to eat more healthy because I had too much cholesterol in my blood. She wrote in front of me a list of things to eat and things to avoid and basically explained me stuff like “spoiler alert: you know, butter = not good”. I was astonished. On top of that, it was written on a note/advert for a cholesterol medication that she probably received from this pharmaceutic group 
. I can laugh about it now because it’s so ridiculous. Especially since high cholesterol can be due to genetics but that’s another topic. 
The sad part of this small interaction is that it convinced me that it wasn’t worth it to reach out. I thought that if what was destroying me wasn’t understood by a doctor, then it would be the same for anyone else. Obviously, I was wrong. But again, I was young and very vulnerable at the moment. I wish I didn’t lose so many years after that.
On the other hand, I had to weight myself once at a doctor’s office (for a very different reason) - they had the result on their computer and asked me if I wanted to know it. This very small question was, in my opinion, an incredible mark of respect. I didn’t expect to have the choice to know or not. And even if it can mean nothing for someone who’s okay with their body, it meant the world for me.
Anyway, as always, it really depends on the doctor and the person in front of us. Thankfully, there are some really good doctors out there!
It’s also really great if you have the intention to discuss about it with your doctor. It shows that, despite the trigger, you are at a moment in your life when you gathered enough strength to stand up for yourself - which is awesome and something you can be absolutely proud of. I think what matters the most when dealing with eating disorders is to learn to accept ourselves progressively, even before any matter of food or weight. Just because feeling better has an impact on the way we eat and just our behavior in general. It creates a positive pattern. Better being overweight but happy and able to eat a little bit of everything than being overweight, starving yourself from time to time and/or binge eating on the crappiest food possible. That’s the invisible side of a weight number or a BMI. But you know it. You know your story and yourself. It’s all that matters in regards of this email you received.
Keep doing good. Take your time. Keep being motivated by discussing and making your doctor understand your own experience. There’s something in your frustration that can be turned into something positive and helpful for both you and your doctor. 
Somehow, the “positive” part with this email is to realize that your doctor needs you on this matter, to be more sensitive to what you’re going through. Communication can be improved.
