I know, I know

I've reconnected with a friend from the past and when thier phone broke they asked me to help get another. They were on a Metro paying $70,per month. I offered to put them on my plan pay less get more benefits and get in on a new phone promo. Phone line is $20 and the promo is a $20 monthly credit that covers the payment on the phone. Every month I have to ask them to pay, well since June I've gotten $20. The phone had insurance at $10 a month that I canceled already. What to do? BTW they only paid the $20 because I suspended the line. What to do? Cancel the 4th line and take the L on the phone. Still owes $350. Also since I'm probably not going to get the back but still pay for it. Can I block it. Can't report stolen that would be fraud. Signed, I know I know