@Strykar First i suggest you to disable pppoe and setup only static.. once you make it work, then enable pppoe for ipv6 and configure bit higher route distance. I guess you cannot have two routes with same distance, from your screenshot i see you have static and pppoe routes have same distance as 1. I usually had distance as 10 for pppoe when using static ip.
Also first make sure, static ip configuration is working your airtel
router provided you got static ip recently. Sometimes, they give static ip, but it never works and they had to do some config in backend to make it work. Ofcourse if you are already using static ip, then this is not applicable for you.
Regarding my nat firewall, i usually create a interface list and all all the wan related interfaces in that. Then in NAT, created single masquerade rule for the interface list like below,
@Sayantan Its difficult to know what could be the problem without you sharing any config/screenshot. I suggest first check whether proper route automatically created for sfp ip range. If its there, then mostly its firewall related rule blocking. Check few posts above by
@anmolbhard004 where he shared complete his working config screenshot. Hope that helps.