If your original Non-O was based on retirement (over 50) you can get a 12 month extension based on retirement by meeting the requirements including having 800k seasoned in a Thai bank account for 2 months prior to application or with an Embassy issued income affidavit
You will no longer be on a Non-B Visa but on an Extension of Stay based on the original Non-B and it is the Extension that must be cancelled - read the conditions you signed when it was granted.
If you keep the 800k make sure you get documentation from the bank covering 12 months and including 12 monthly deposits of 65k and highlight these on the 12 month statement so that the IO is aware that this is the reason you are applying for the new extension
I don't think that you are on a Non-B visa for the last two years. Look at the latest stamp in your passport which probably stays "Extension of Stay Permirred up to _____" just like this