educator upgrade

Hello THank you for your service.

I'm a teacher of South Korea.

My account was originally educator account so I got free upgrade and could have a class more than 40 min.

But Yesterday when I tried  online class, I and my students shut off after 40 min. 

I tried to find out solution so checked up educator section but it didn't work. 

I have to have online classes for a week due to Covid quarantine. Please help me. Thank you.