I was charged twice after I changed my plan

I joined my friend's multiline service last month and today she renewed the plan by paying totally $110  for both of us. Right now,  I was charged $30 again through my own card Autopay!

I cannot find any support for this problem. There is no online chatting option for prepaid plan and the phone number provided was answered by a robot which only asks you to change plans or add more data!

I feel confused...