What can I do if my extension based on marriage in Thailand was denied after a work permit cancellation?

Okay let's discuss this. Earlier this week I failed to obtain my extension based on Thai marriage, and I'd like to know other's experiences to understand what went wrong.

Employment until January 29. Work permit and extension based on employment cancelled on January 29 by the company agent. Passport returned on January 30. Immigrations Chamchuri Square gave me a 21 day stamp 'to leave the country'. My work, the agent, and even officers are Chamchuri Square, all confirmed to me that this 21 day stamp CAN be changed to an extension based on marriage with Thai spouse. Had both read and heard that Cheangwatthana would require 21 days for this thing, but heard that they would give an "under consideration" stamp, from a usually exceptionally reliable source on Thai visa matters.

Made appointment with Cheangwatthana for the said extension, earliest opportunity at a convenient time (going with a minor) was Monday 12 February. Extension failed. Not only was the list of documents given by my employer hopelessly incomplete (that was a calculated risk; didn't go on the last day for this exact reason); no the real problem here was that they outright denied that the 21 day BOI status Chamchuri Square stamp did not qualify for switching. Went higher up a few times and in the end had four different officers all tell me the same thing: that stamp can NOT be switched.

The same exceptionally reliable source I referred to above told me that it was the weirdest thing he ever heard in all his dealings with Thai immigrations in his entire life (and he probably dealt more with them than anyone else who has ever lived). He said that probably a handful of the people sitting around me at that exact time would have the exact same stamp in their passport as I had, and would get the said extension without issue. Other sources who are usually similarly reliable have however told me the opposite, so fair to say, I'm confused.

In the end my company intervened and negotiated a 60 day extension based on visiting Thai family.

Maybe last thing to add: immigrations officers said also that switching to spouse extension from anything that wasn't non-immigrant type O was not possible. So as if we're back to the days without switching reason to stay, when we could only change reasons by going abroad. This somewhat improbable claim makes me still doubt whether their call to deny me the extension because that particular stamp wasn't good for switching was at all right.

So I do not really know what my rights were at the time. Do they normally switch that 21 days stamp from Chamchuri Square to other extension types? Or not? Was the mistake to cancel the WP and work-based extension on the last day? Would they change extensions then? Does it require having 15 days remaining (the 21 days that I saw on the immigrations website turned out to be 15 instead so could have gone in the first days of my 21 days Chamchuri stamp in retrospect). Have they stopped doing extensions for spouse with anything other than non-O perhaps since this year?

Any experiences/insights are welcome.