If they can't even tell a citizen what needs to be done in order to straighten out a visa application
U.S. citizens do not need visas.
In the OP's case, I think it is his brother-in-law - who one assumes is a Thai subject - who is applying for a visa. Clearly applicants need to be able to sort out their own issues.
Based on the hundreds of Thais I see lined up outside the U.S. Embassy on Wireless Road each morning, and the fact that there are ~ 350,000 Thais who've legally emigrated to the U.S., I can't see local staff providing personalized services for local U.S. citizens who have relations seeking a U.S. visa?
Again, I wish we all could get the level ("basic" or otherwise) of service we want and expect, but I doubt that that can be delivered, nor do I believe that it is reasonable to expect it. BTW, we're not alone in our dissatisfaction; nearly every foreigner here has complained about this "issue".
Finally, asking your Congress-person to help sort this out will, in most cases, make the matter worse.