Long story short. I’ve added one number wearable plan to my cellular watch and can now not receive incoming calls on my iPhone. 
If watch and phone are on - nothing straight to voicemail
If phone is off and watch is on - the watch will ring. 
I’ve been round the block with Spark who say there is nothing wrong and have now told me to go into a store and change my esim on my iPhone to another one. 

I can use data. Make calls. Receive incoming and outgoing texts.