I think IPs may change according to location. I am from kerala so mine might be configured to connect to BSNL's systems for my area. Also, you shared voice interface(IPoE) details and I shared internet (PPPoE) details. It doesn't allow me to see the IPoE settings like it shows PPPoE settings.
After this was posted, I looked again at my voice WAN config and realized its Service Mode was set to VOICE. So I changed it to VOICE_INTERNET and voila I can ping the voice gateway but not SIP server. So a static route needs to be made. Network -> Router -> Static Route and do the necessary changes.
Destination is the SIP server address, Gateway is voice gateway. And we are connected.
Things I did differently than the linked post. Disabled SIP under Application -> ALG configuration. Routers SIP ALG - VoIP-Info.