I have found basically two problems.
First the routers must have routes. On router branchR, you need to add one route telling him how to reach the router 8.8.8.8
I did with static route.
ip route 0.0.0.0 0.0.0.0 203.165.200.1
As 203.165.200.1is the ISP, it does make sense send all traffic to there.
Another problem I have found is ACL. You have the following ACL on the ISP router. This ACL is denying the traffic from 192.168.0.0 0.0.255.255 which include your local network which is 192.168.88.0.
!
ip access-list extended FILTER_PRIVATE_ADDRESS
deny ip 10.0.0.0 0.0.0.255 any
deny ip 172.16.0.0 0.15.255.255 any
deny ip 192.168.0.0 0.0.255.255 any
permit ip any any
!
I removed the line "deny ip 192.168.0.0 0.0.255.255 any"
Now is pinging.
