What should I do if I can't obtain a letter of appointment for my DTV visa in Hua Hin?

So I am wanting to pursue a DTV visa for medical reasons, using some chronic conditions I have (psoriasis and it's accompanying arthritis) for ongoing appointments etc.

I have run into an issue with the primary hospital in the area I'm looking at staying (hua hin) flat out refusing to provide a 'letter of appointment' or 'advance continuous scheduling' (which I take to mean more than one future appointment).

Does anyone have any recommendations for how to handle this? Are there any other options for the paperwork I would need?

I've heard good things about the traditional medicine, would those clinics count as sufficient for the visa needs? Are there any in the hua hin area?