These replies often confuse. So most people turn to am agent for reassurance. Particularly in Samui where the immigration office is hideous. But I would suggest this. Come on a visa on arrival if you can. Deposit the money 800 k now and leave it. Go to Surat Thani immigration with your bank books. They will advise the rest. Take a visit to them, do as they ask, they will issue the non o. Easy. Samui will not. You don't need to go out of country. Ask them and you will see. You defo do not need to spend 40k on corrupt agents.
People overlook the most important aspect, which is not even asked in the application process. You concentrate on answering the questions and providing evidence of relationship and your good standing in your home country. But the only thing the consular services look for is a compelling reason to return to Thailand. For example job, house, family, bank accounts, commitments, obligations etc.. Without that, your millions in the bank, large house and 20 year relationship is more likely to garner refusal because why indeed would she want to return. The humble application from a not so well off person applying for a girl who has lots in Thailand is way more likely to succeed than the millionaire taking a pauper. Visit visa’s have been abused so much that now you have to prove you will return. Photos of the two of you on a beach don’t cut it.
If you go to immigration and tell them your story they will advise. They are being pretty understanding and I’m sure with your evidence of flight they will just let you extend. Don’t do overstay of you want to come back.