The WAN IP is 82.129.xxx.xxx, not 192.168.100.254. This is essentially the cause of your woes. This means there is a router between the public IP and 192.168.100.0 and another between this and 192.168.0.0, which is the cause of double NAT.
Earlier, you said…
Is that the “little box”, or something else? Please confirm, thanks.
Otherwise, if there are no other devices between the microwave dish/antenna and the Archer, then the ISP will need to resolve this since there is nothing you can do.