Well done I'm still awaiting my approval ? Submitted on the 21st June, all docs checked and has been awaiting approval now for 5 days!!. Can't see a contact email to ask the thai embassy if there is an issue?
as John says you can extend in thailand but for this extension I.e. after the 2 years if you get your timing right you will also need a thai bank account with the 800k deposited aswell as the mandatory insurance
you leave thailand near the end of the first year then reenter before your visa expires with a new year's insurance, you will then get a new 1 year stamp aligned to your insurance end date. Also you will need to get a re entry stamp as the second year is a single entry not like the first year which is multi entry
an O extension needs the money in a thai bank account. The O-A is good for 2 years without money being in a thai account. So although bith need to demonstrate 800kbaht or 65k baht monthly income, the O-A allows you to use your own account in your own country of residence in your own currency
You should be able to look up what the system accepts. So you might find you are putting the address in incorrectly? Thai systems aren't always sensible!!