Your story is lacking crucial information: What is the agency name (FB)? What visa were you trying to extend? What mode of communication did you have with them? Do they have a physical office in Thailand? etc.
Khon Kaen is considered a "red zone". Took 45 min to get to Bangkok, but 7 hours bus back to Khon Kaen, lol! p.s: Train also require PCR or vaccination back to KK.
Each province has different regulations. For example, I recently flew from Khon Kaen to Bangkok and you don't have to do or show anything (you don't even need to be vaccinated), but to get back to Khon Kaen you need to be vaccinated.
The ed visa with agent will be available again in June or July. And no, they are not fake, it's real stamp from real officer. Getting a bribe does not mean that the stamp are fake.
I agree about ruling and implementation being inconsistent. BUT... in a situation like the one Garrett was in, he handle it the way I would and I've been in Thailand for a very long time. This is the kind of "grinding mentality" that you need in Thai hospital, immigration, police checkpoint, etc.