Video/Audio calls not working

Hi Team

   Since 2 weeks I have troubles with calls (video/audio) on TEAMS (desktop version):

When I call, I get this error message (I can't attach screen shots):

Sorry, we couldn't connect you

  When anyone calls me it goes straight away to the voicemail box even if my TEAMS is active and online. I don't see any incoming calls(audio/video) 

   I noticed also that :

 - I see missed calls after that on my desk version for the call I didn't see.

- Even when my desk TEAMS is active, I still get TEAMS calls on my cell

- If I disable notification on my TEAMS on my cell, I still don't get any call on TEAMS on my desk

- The web version is working on my desk but I can't use it because the share screen is too small.

This is what I've done so far:

- I made sure my Windows 10 is up to date (10.0.19044)

- I made sure TEAM is up to date as well : 1.5.00.28567

- I restarted the computer

- I deleted all TEAMS cache %appdata%\Microsoft\Teams

- Uninstall and install TEAMS from scratch

- I made sure that the option Calls ring me is selected on TEAMS on my desk

- I made sure that the option When active on desktop is blocked on my TEAM on my cell (Notification\Block notification )

- I made sure that in Office 365 administration center, coexistence mode is set to Teams Only

- I made sure that in Office 365 administration center, the voice routing is by default (same as my colleagues)

Regards