Xfinity Mobile Account Restoration

My son was traveling overseas this summer and I was advised by an xfinity agent that we could upgrade him to an unlimited plan allowing overseas data.  He was traveling for a couple of months.  I noticed his bill had gone up so I tried to switch him back to by the gig today because when he's studying at his Scottish university, he doesn't use his line.  But now I'm informed we only had 30 days to revert! This would have been impossible in any case since he traveled greater than 30 days.  I don't appreciate being lied to, and customer service won't escalate to a supervisor.  I'm a diamond member and pay a rather large amount monthly for my xfinity services.  I'm so unhappy that I'm researching cutting the cable altogether.  However, if there is a different channel to have his mobile account (which is on my account) restored, that would be great.