I solved the issue. Siproxd was sending UDP packets via the WAN default gateway (INTERNET). Previously I had a static route to BSNLs VoIP network. I removed the default route to the Internet and made the VoIP gateway as the default gateway.
Also, I could make the VPN work by adding a specific/static route to my VPN server. But I can't reach whole of the internet from my pi. I may have to create two separate routing tables. Happy that VoIP works. Latency is pretty bad. Nothing can be done about it. I'm on a different carrier on my phone.
Also, I could make the VPN work by adding a specific/static route to my VPN server. But I can't reach whole of the internet from my pi. I may have to create two separate routing tables. Happy that VoIP works. Latency is pretty bad. Nothing can be done about it. I'm on a different carrier on my phone.