How to drop DHCP request packets on a bridge (2 lan)

I have Sophos xg 135, #Port7 and #port8 are configured as a bridge for internal lan, #port2 as WAN for external

I want to drop all DHCP request on the bridge.

Already configured a rule to drop DHCP service on the bridge (which is not dropping dhcp requests) as follow: 

Source zones ----> Internal_LAN (#port7+#port8)

Source networks and devices ----> Any

Destination zone ----> Internal_LAN 

Destination networks ----> Any

Services ----> DHCP, ICMP

I added the ICMP service for testing purpose, tried to ping local computer from #port7 to #port8 and ping was successfull

Under  at the bottom an allow rule from any to any is configured

Can someone advise please

Thank you