SIP media problem [Asterisk]

Hello!

I have installed a Cloud FreePBX server [Fully configured] SIP with TLS
But the user's location is in a country that has SIP Traffic restrictions (Blockage)
Everything is working and the calls go through 2 SIP Extensions but there is something wrong with the voice!
The voice is like shaking!

Note 1: If I use a VPN to avoid the SIP traffic restrictions, the voice is so clear and there is no such problem in the call

I think may one of the following ideas are resolving the problem:
1- Install & Configure a Cloud SIP Outbound Proxy Server like Kamailio or any other SIP Outbound Proxy Server
2- Install & Configure a Cloud Stun/Turn Server
Note 2: I can provide a Cloud VPS server to use as you need to solve the problem

Note 3:
1- It's up to you to resolve the problem with any perfect method
2- Awarded will be to the one have an experience only to complete this project successful (no wasting time)
3- If the project is done perfectly in max (48 hours), a bonus will be added

Thanks to all who will bid on this project!