My experience with the Thai tax people is much the same, ie, they are helpful, friendly and most cooperative. In the same situation, I'd surely consider a trip to the Ministry of Finance with the dumb and befuddled farang act in tow.
When I was in Satun province I had to see the Finance Ministry people in Satun City and cordially was taken to the director's office, where everything was warm and fuzzy.The director and I were taken however to find I'd been individually entered into their computer system more than 300 times! So maybe they're not so competent.
Anyway, the director, who has a certificate from the outstanding Wharton School of Business & Finance at the U of Pennsylvania in the US and who speaks excellent English, cleared matters up, took care of business and then gave me a ride 20km to the locale in Satun where I had my residence and my after school hours and weekends school. Mighty nice of her, I do say.
As for payment of taxes on farang teachers, at one school where I taught "for a long time" the school said they paid the taxes directly for me (and each farang teacher). Each year each farang teacher got a signed statement from the school which itemized the amount of taxes paid, a document a farang teacher needs to have on file when applying for another teaching position in Thailand.
Further, Immigration requires a record of such payment when a farang leaves Thailand on an expired visa...it has to show up on the computer, at least at the airport. (Dunno about leaving by train or bus.)