IPhone 12 Pro has started to play sounds through it's speakers when connected to MFi hearing aids

When I first got my Oticon Bluetooth MFi hearing aids and connected to my IPhone 12 Pro all audio and notifications were routed through to the aids and the phone itself was silent, which I absolutely loved. I didn't have to worry about other people reminding me that my phones was ringing, nor did I have to switch to silent. Something has now changed and my phone now plays ringtones and some messaging alert at the same time as in the aids. I've searched settings, talked to apple support but no one know why or what has changed.

I've tried the mute switch on the side but that also mutes some apps playing to the aids.

I don't use the Oticon app just straight in with the IPhone's MFi connectivity. Oddly the aids don't show up a Bluetooth device but are connected using Bluetooth.

Was I utilizing a bug in software which has been fixed, or is there a setting I've missed?