You would report a problem with the session and when under the drop down menu you can request a refund or to reschedule a session. I try to show up at all of my sessions but if there is a problem, such as student having problems disconnecting, then I will usually as a teacher issue a refund automatically and the student can then reschedule if he/she desires to do so. The teacher should be instrumental and proactive in making sure that you- the student (i.e. the customer) - receives the best quality service possible.