When he got his own plan, did he keep his same number?  Did he assume liability of his line with Veriozn?  Or did he go with a totally different company?  If he ported his number to another company/carrier, you will be getting the ETF charged to your account, and I would put that back to him - since he's the one that cancelled the line.

If he simply opened a new account with a new number on another carrier or even on Verizon, then you can put a basic phone on the line and reduce the charge to $10 and texes (if on a family share nationwide plan) - or perhaps find someone else to assume the line and make it their own.

He *should* have consulted you can could have done an AOL to take over the line, keeping his number, and avoiding cancelling the line altogether.  I think it's too late for that, so your choices would be to reduce the cost of that line as much as possible, or find someone to take over.  Unless, of course, he ported the number and then it should be up to him to cover the ETF.  But that's between family members....