Extremely hard to say, since the big question is how your record has been documented. That's likely to have a strong influence on whoever you speak to next. However:

1) The change of the first 2 segments to a reasonable CAI-XXX-BKK is totally permitted free of charge. They're wrong there. Now, how much change is reasonable is at the mercy of the agent, but you are being totally reasonable to ask for anything "closer" to your original date than the 24 hr change they've offered you. Changing it by weeks? That might not fly without a refare, since they'll potentially argue you're changing more than the "forced" change.

2) Now that you've changed the other segments, you're in a bit of a pickle.. Asking them to put everything back as it was is a major ask, and unlikely to happen. Your best arguement is "your agent told me I could" but I've rarely seen that strategy work - unless you find the right sympathetic elite agent.\

All that said, now that the "mess" is made, a good agent will work with you to clean it up. Recognizing these fares WERE a steal, you're likely going to have to settle on "good enough" as opposed to perfect at this stage. Even changes to future segments can get messy with low-quality agents, so it's truly a case of having to put in some effort to get the deal to work. For now, if I were in your place, I would focus on getting something reissued that's at least acceptable to you with no upcharge. The more you fight for perfect, the less you are to get it in my opinion.