Your IT person, isn't as smart as he wants you to believe. You can upload the different files in parts or even file by file. When you have an lousy connection only an idiot would try to do the whole bunch in 1 go.
Like many others already said, if you tell the reception your problem, they will send you to a specialist. If you know what sort of doctor you need to see, you book one online.
You can ask you HR or Finance department to help with your yearly tax declaration, done between February - April. On that tax form you can declare your Estonian income besides your Thai income. Then you will get a paper from the tax department what tax you still need to pay. This can be done in one go or you can pay equal parts in 3 months time.
It would be nice if you actually read his comments:
"She could apply for a non-o visa at a nearby embassy or consulate with supporting documents from the organization." So she can do both.