please check and help to reply at earliest.
What type of Voip account are you using?
Is it SIP or IAX2? Obtain this information from your VoIP provider or system administrator.
If your report is concerning audio related issues - what audio codecs
are you using?
ANS: audio is not audible one sided while connect on VPN
Are you able to recreate the issue every time you try?
ANS: no need to create issue exterenally , it is happening always while connected with VPN
Is it the first time when the issue appears?
ANS:no , it's very old.