Can I extend my Non B visa in Thailand and apply for a new one while back in South Africa?

Good morning All.

My Non B visa expires at the beginning of December , and I am planning on going back home for the holidays(SA). I have a work permit.. Will I be able to extend my Non B visa( in Thailand) till the end of December, And then apply for a new one when I return in January.

I was also advised that I should apply for my Non B visa in SA before I return to Thailand . ( is this correct)

Thank you in advance.