It's a very grey area, some folks said that once you got a dtv then nobody would know whether you got it through soft power or work. Some others said that while you can work online/from remote legally if you applied for, it's still illegal to work if you have applied for soft powers
Since you can provide the registration letter and your 350euro are gone, I'd try to write a cover letter (chatgpt is your good friend) stating that according to the law in your country you aren't supposed to have any but then you should be able to prove that money from your clients goes regularly into your bank account. I'd also send portfolios, example of your previous jobs, emails with your clients and whatever can support the fact you're a freelancer. Even that might not be enough but at least you tried
obsolete for those ones who are on a budget, elite visa has no taxes if u bring money from abroad and this seems fit op perfectly... If I had money I'd go 100% on elite
Cancelled means you didn't fill the application properly, wrote something incorrectly or didn't include the required documents. It's hard to understand what happened from your post
If they didn't reply you then it means they can't reschedule. By claiming u got an urgent meeting in Thailand is going to bring your application to get rejected, u can't conduct any sort of physical business in Thailand, even with the DTV. Is that meeting more important than 10k spent for the application? If yes then go for it and then apply again in Vietnam otherwise u just move your meeting