What did you submit for this requirement?: "English portfolio....providing your life plan"? Did you give an explanation of how you'd support yourself or how you'd occupy yourself in Thailand? That is how I'd interpret this.
The requirement for soft power, for most embassies, is an appointment letter, with no guidelines as to format. OP's mistake was asking for a letter for the DTV in his first contact, which now makes the healthcare provider worried about reputation management.
I got a DTV for medical treatment myself, but I didn't involve my care provider in visa issues. The provider says that they only will provide a letter for a DTV for a patient who's only been in their care for over a year among other requirements that the OP can't meet right now. The hospital didn't say that they wouldn't provide any treatment plan at all, just not for DTV applications, which personally I don't think is their call because their expertise is not immigration.
My point is anyway that there's nothing stopping the OP from bypassing their refusal and using other treatment documents they provide, which they could obtain with a medical visa or otherwise.
Also, the hospital's answer specifically relates to patients "eligible to apply for the DTV," not whether they would be able to seek treatment at the hospital.
Is there something stopping him from registering as a patient at the hospital and then receiving the documentation? Is the issue that he needs to DTV to enter Thailand at all based on his nationality?
I don't know why the medical provider would be in the position to determine eligibility for a visa. They can decide what treatment you need and it would be up to the embassy to decide this based on the facts, no? Are they refusing treatment because you're not on a proper visa yet?
Anonymous participant I have a hyphen in my first given name as well, and when the system captured it, and it's displayed differently on the biographical page on the passport. In the MRZ (machine-readable zone), it omits the hyphen, but my full name above shows it. The OCR in the e-visa application system separated my first name into first and middle incorrectly and left out the middle name. I corrected the first name but didn't input my middle name. Didn't think omissions of non-essential (in some cases) parts of your name were errors. Actually didn't think my middle name is important for a visa. So, yeah, I got rejected but ended up getting accepted later. I also don't agree with it, and it isn't common to take large application fees for minor errors in other countries, despite the vigorous defense this topic seems to provoke here.
Anonymous participant 561 I know, let's get over the idea that it's just fabrication. And why don't people just invent these false stories about Bangkok then, not just Chiang Mai?