You don't actually take a class directly in iTalki, you only book lessons and confirm lesson completion. That can easily be done on the mobile app using mobile data. The classes are typically on Skype and even that can be done with the Skype mobile app using mobile data or WiFi. In fact I often do that myself. This comment is also written from the mobile app using mobile data.

Skype is blocked in the UAE. That's why I'm asking if I can use mobile data in italki classroom during the class