In your current settings, eth0 is tagged "option ports '1 6t'" this connects the WAN labeled physical port to the switch hardware untagged, but sends the packet to the CPU tagged (the switch tags it).
Instead you need the WAN port to send things tagged because that's what your ISP wants. and it wants them tagged with VLAN 7. One correct way to do this is:
option ports '1t 6t'
and then make the WAN "interface" connect to eth0.7
another option is to make port 6 (eth0) untagged, and make WAN interface connect to simply "eth0", since it only interacts with one VLAN and it's therefore unambiguous. The switch hardware will stick the tag on when it goes out the WAN port. But I don't recommend this, I generally used tagged interfaces on infrastructure equipment where possible (ie. routers, switches, APs etc)