Zoom says I have a meeting running when I don't

I'm trying to start a scheduled meeting but Zoom says I have another meeting running (which I don't) and asks me to end it. When I do I get a message from a colleague that his meeting just died. When he tries to re-start he get s the same message and when he ends "the other meeting" my meeting dies.

We both hold separate licences and our clients are not very happy!!

Any suggestions? We have both quit and restarted our Macs, and my colleague set up a new 'clean' meeting that i wasn't invited too, yet the issue persists...