@Ju***
you can't "renew" a visa or an extension either :/ .
A visa <- that you buy from a thai consulate in another country expires and then you go BUY a new one
Same thing for your extension from the immigration ofifce, you apply for it, it's good for how long it's good for and then it runs out and you apply for a NEW extension.
I think your sponsor is confused and you should go to the immigration office that you got your extension from and see what documents you need to get a new yearly extension inside the country.