Will I have to leave Thailand by September 26th if the amnesty ends?

@Rainer *************

, you have extremely limited options.

As

@Mar***

correctly stated is; bank 800K baht in a thai bank account in your name only for 2 months before you apply for a yearly extension based on being over 50 at the immigiration office

That meant in order to NOT run on overstay (and be fined 500 baht a day until your money is seasoned and you can apply for the extension ) you needed the money in the account on July 26th (July 26 - Sept 26 = 2months)

OR

You need to "prepare to depart" the country on or by the 26th of Sept when the amnesty runs out.

I am making no judgement on you or your situation BUT if the truth be told; you've been IN the country since the end of March (almost five MONTHS, you should have started looking into the options you had a while ago.

As I see it those are your choices..

Very easy, just follow Benjamins instructions. I did the same recentlly in Chanthaburi. It just took 10 minutes and Passport pickup was next day

If you have the necessary funds (800k for retirement) for 2 months in a Thai bank account in your name, you could apply for a yearly extension of stay without leaving the country.

What reason was your multiple entry Non-o visa based off of?