@YiannisH_3CX whilst prepping to submit everything over to you, I deleted all the ring groups, dummy extensions and forwarding rules and did it all again.
I figured out why the forwarding rules weren't working.
On both dummy extensions I had "Announce Caller (Rebound)" enabled.
When enabled, calls from ring groups seem to be completely ignored.
Obviously when disabled, it all functions correctly - annoyed I didn't figure this out earlier.
@Luis Londono did you also have it enabled?
Just to clarify:
All dummy extensions are set to status away.
All dummy extensions have forwarding rules under the away status.
All dummy extensions are configured to accept calls from ring groups.
So now the question remains...
How do I forward the call to a mobile device whilst announcing/screening the call to ensure that the VM/out of service doesn't pick it up and ruin the flow of the ring group?