I pay for zoom monthly and they are interrupting my classes in 40 min

Welcome to the Zoom Community, @FabioNemer.

If you have a license assigned to your user account, you shouldn't be interrupted.  

You might just need to assign your existing license to your user account. See this web page for assistance:

https://support.zoom.us/hc/en-us/articles/115004976063-Assigning-a-License

Follow these steps taken from the article:

1. Sign in to the Zoom web portal at https://zoom.us.
2. Click User Management, then Users.
3. Locate or search for the user who you want to assign a license. There will likely only be your single account – click your account
4. Click Edit at the end of the user row. This will open a window.
5. Choose the User Type to assign, selecting Licensed.
6. After choosing the User Type, use the drop down to select the license. There should be an indication that you have 1 available user license if you have indeed purchased one or more new licenses. Click the available license.
7. (Optional) Assign add-ons can be included by checking the boxes for the add-on. You will not likely have any add-ons, so you might skip this step.
8. Click Save.

The license is now applied to your user account and you can use it immediately.

If this does not fix your issue, please submit a support ticket to our Billing team here and they should be able to assist you.

https://support.zoom.us/hc/en-us/requests/new?ticket_form_id=360000983032