No sound on quiet comfort 35II

I've had a pair of the Bose quiet comfort 35 II for around 6 months and just recently they have started to connect fine but have no sound. They are connected, I hear the audio cues for the battery life etc and it is paired and connected to my phone but there's no sound.

I've tried resetting (it didn't return to factory settings), unpairing and pairing, using different media apps and all sorts. Can't work out what's wrong! Any advice would be greatly appreciated