I can't help with the answer, but I can suggest where to look.
Somewhere in the router's firewall
settings there should be one for either (Reply to) Ping or ICMP Echo. That needs to be enabled.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. 200GB. Sync 72313/12530Kbps @ 600m. BQMs - IPv4