I have a valid NonO by marriage valid till Nov2020 but the stamp says i must leave by April12 (should be 90 days but actually erronously 60 days stamp given on my last arrival) . Sorry for silly question because i have never done a '90 day report' because i always leave the country every 90 days and come back in anyway... Can i do any sort of online report or must i visit immigration?

 

I am under the impression your first 90 day has to be done in person. Thereafter in person, post or online. 

You apparently have a multiple entry non-o visa that allows you to get a 90 day permit to stay every time you enter the country.

You have to leave the country every 90 days to get a new 90 day entry.

To do a report of staying longer than 90 consecutive days in the country you have to have a visa or extension of stay that allows you remain in the country for longer than 90 days.

If they only stamped into the country for 60 days the last time you entered the country you can go to a immigration office and have the error corrected. 

Then if you want to stay longer you can apply for a 60 day extension to visit your wife.

You can go to your local immigration office to get the erroneous entry stamp corrected.

 

You don't say what the purpose of your trip to Thailand with the non-O visa was. Depending on your circumstances you may be able to get a 90-day extension of stay from the immigration office.