You seem to have the correct files everywhere, and pinging remote IPs says you are online.

Maybe your provider enforces their own DNS servers (some do). Try to copy the dns servers that pppd receives (103.8.45.5/103.8.45.6), and put them in either /var/run/resolv.conf or /var/run/resolv.conf.ppp0

Also, just test if you can resolve domain names using dig or nslookup, e.g.