Android dual sim no microphone

Nothing is so annoying as a microphone from a smartphone that's not working.

In my case I had a dual sim setup on a samsung galaxy s20. With sim1 everything was working fine, With sim2, I could take calls (that went well) but when I wanted to make a call, certainly over bluetooth) things got messed up. Or the mic wasn't working, or the connection was made at the other side but the phone was still ringing at my side.

how to fix this?

1. try turning off your bluetooth to validate that that isn't the problem
2. turn off wifi calling (phone => settings => wifi calling) for the sim with the issue
3. turn off volte (settings =< network => voice over lte) 
4. test if it works
5. turn bluetooth back on and retest

nb, it could also be that proximus (mcarrier) doesn't support volte but I assume its a combo of samsung and proximus both as this was working befre.