NOW Internet Issue

I activated my xfinity NOW internet today paid $30 that is good for 30 days. Then few hours later, I noticed that my internet is not online, so I logged in to my xfinity NOW app to restart the modem, then all of a sudden it says no service and I received email saying my service got disconnected. Xfinity NOW assistant doesnt even know why this happened and wanted me to pay another $30 to reactivate. I need help so that this not happen again. I just lost $30, But I truly do not know what to do when this happens again. Please help me.