Stop ring all when one of the extension is unavailable


I use asterisk 11.5.1 with freepbx

Is there any possibility to stop ringall when one of the ring group extension is unavailable?

I forward one of the two main extensions (x), that receive all external incomings calls, to another (y) that is unavailable and play a voicemail message, but I can’t reach y because x is in the same ring group of the second main extension (z) that continue to ring, even if x is forwarded.

Thank you

Can someone help me?
I will change the question:
Can I hang up an incoming call when only one of the call group extension is unavailable?
I need this because when anyone is in the office, the calls are redirect to an unavailable extension that answer with a particular voicemail message, but I make the redirection from one of the extension of the callgroup, I can’t ask users to do it from all extensions of the ring group.

Thank you