Iphone 6s not ringing with incoming messenger calls

Hi,

I have an iphone 6s which does not ring with incoming facebook messenger calls. Instead I receive a notification saying I've missed a call.

I've checked all the usual settings ie - do not disturb is not on and all the sound settings are correct. I've scoured the internet but I can't find an answer.

I'm not sure if it's relevant but it did work fine... Then I connected my apple watch and this is when the problem started. I've tried turning the blue tooth off while at home, so both items were connected to the internet via wifi but that didn't seem to make a difference.

Anybody any suggestions please.......

(Oh and I don't know if it's relevant but they are international messenger calls.)