How to invite PSTN Phone to Skype conference via participator number,not use organizer's number.

Here is the background for the issue:

User A:  Skype for business meeting Organizer   [Enterprise voice enable and DID number enable]

User B:  Skype for business meeting Participator [Enterprise voice enable and DID number enable]

User C:  PSTN's mobile phone

When A and B are in a meeting. they want to C to join the meeting and discuss something.

So, B invites C to join the meeting(click the button [invite more people] and type the phone number).

At this time, C's mobile phone is ringing. 

And here is the issue. C's mobile phone's display number is A' DID number which is meeting Organizer. Not B's DID number. but actually, the caller is B.

and I had some troubleshooting for this.  step as below.

1. Disable the User A's Enterprise voice and delete the DID number in his user profile.

Try to let B test to invite C 

Error with the call cannot found and dial out failed.

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2. Enable the User A's Enterprise voice and add the DID number back to his user profile.

    Disable the User B's Enterprise voice and delete the DID number in his user profile.

Try to let B test to invite C

C's mobile phone's display number is A' DID number and join meeting successfully.

3. Enable the User A's Enterprise voice and add the DID number back to his user profile and let user A quit the meeting.

Try to let B test to invite C

C's mobile phone's display number is A' DID number and join meeting successfully.

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4. Enable B's Enterprise voice and add the DID number back to his user profile.

Quit the meeting and dial C directly.

C's mobile phone's display number is B'DID number and call successfully.

About two weeks ago. this is no issue here. not sure why it happened.

All the call in the meeting seems like base on the Organizer number. not callers.

Anyone can help?  Thank in advance!