What documents are needed for visa extension at Wattana immigration for a Non-O-A visa?

The immigration office can't help you because you can't apply for an extension until you have 30 days or less left on your current stamp AND your current stamp is valid until 26th March 2020 :O That's why they don't know what you're wanting to do..

You are good to stay here until 26th March 2020. As I said IF you are going to leave and come back during that time you NEED to buy a re-entry permit (either a single re-entry for 1000baht or a multiple re-entry for 3800baht)

If you leave without buying a re-entry permit before hand the stamp you have now will cancel..

Okay, now we know what's what. You had an O-A visa valid from April 2018 until April 2019. You exited and re-entered the country in March and were stamped in until March 26th 2020. <- if you are going to leave the country between now and then you need to BUY a re-entry permit.

BUT you do NOT need to apply for an extension until the end of Feb 2020. In fact you CANNOT apply for an extension until then.

ONE LAST TIME. What is the "enter before date on the VISA itself (the one you got from France)

okay, you have a year-long, multi-entry Non-O-A (Long Stay) visa that you got in France before you came here right?

IF that is correct what is the "enter before" date on the VISA itself?

Works at CMAS, studied at PADI, lives in Bangkok, best option is to ask your employer to pick up the list with requirements for the Extension of Stay based on working in Thailand. It is a long list and it could differ at different Immigration Offices, so the best is a current new list from your Immigration Office.

How about starting with stating the country your passport comes from, what type of visa you're on now, and what type of extension you want to get ?

Based on what?