Uninvited attendees gate crashing Teams meeting

We are having this happen by the same person each time, the are a known (external) occasional guest, but they appear in the waiting room to meetings they have not been invited too, we have also checked that the link has not forwarded to them which it hasn't. this seems to coincide when the uninvited guest phones someone in the meeting via Cisco Jabber, obviously they don't answer the call, a short time after they appear in the waiting room.

Is it possible that Jabber can share the meeting request????

We are a tad stumped with this one 

Cheers 

Gerard