I dont really know how it works, I have never used it myself. If I could install the package I would provide more details on how to use it.
If you have the package then LuCI should have the correct protocol in place. Just go to the WAN interface and edit it and choose the IPOA protocol instead of the Static one. I am not sure how it will display in there. Then choose change protocol and after that if you dont know how to proceed then please provide screenshots.
They are also using VDSL instead of ADSL (which I have), not sure if you have VDSL or ADSL.
I think you dont have ADSL line plugged into W8980 at the moment and this is why it shows DOWN status in DSL. Anyway I think there is no LuCI support for IPoA in OpenWrt or so it seems to me (I could be wrong) because when you list luci-proto you only get this:
opkg find luci-proto*
luci-proto-3g - git-19.086.62748-9dd2927-1 - Support for 3G
luci-proto-hnet - git-19.086.62748-9dd2927-1 - Support for hnet
luci-proto-ipip - git-19.086.62748-9dd2927-1 - Support for IPIP tunnels (IPv4-in-IPv4 RFC2003)
luci-proto-ipv6 - git-19.086.62748-9dd2927-1 - Support for DHCPv6/6in4/6to4/6rd/DS-Lite
luci-proto-ncm - git-19.086.62748-9dd2927-1 - Support for NCM
luci-proto-openconnect - git-19.086.62748-9dd2927-1 - Support for OpenConnect VPN
luci-proto-ppp - git-19.086.62748-9dd2927-1 - Support for PPP/PPPoE/PPPoA/PPtP
luci-proto-pppossh - git-19.086.62748-9dd2927-1 - Support for pppossh
luci-proto-qmi - git-19.086.62748-9dd2927-1 - Support for QMI
luci-proto-relay - git-19.086.62748-9dd2927-1 - Support for relayd pseudo bridges
luci-proto-vpnc - git-19.086.62748-9dd2927-1 - Support for VPNC VPN
luci-proto-wireguard - git-19.086.62748-9dd2927-1 - Support for WireGuard VPN
root@AP254:~#
It doesnt list IPoATM so I think this is the reason why you dont see a protocol in LuCI and unfortunately there seems to be no documentation about it so maybe some of the developers can provide more information on how to set it up through SSH within network config.
For now you can try this to be able to use internet without double NAT issues.
Btw can you post a screenshot with all the protocols available in WAN interface? Just click on the drop-down menu and grab a screenshot of the protocols listed.
I think it should be possible to use ipoa through network config but there's no documentation about it. Create a post in the developers section and ask for ipoa config and someone maybe able to help you there.
Are you sure that you have Annex A and not Annex B? I think you should try to change the ADSL mode to Annex A+L+M and then reboot the router and connect the line and see if it works. If it still doesn't work then change to Annex B and reboot the router again. Also try to uss auto values wherever you can.
Edit: So while looking for documentation I came across PPPoA and it seems that in this mode you need to remove the VCI and VPI values and config altogether to make it work (I'm not sure if it is entirely accurate). Could this also be the case for IPoA?
You need to do some toubleshooting first
Check with your ISP that your line is active.
Do the usual like checking ADSL filter, trying different phone sockets and use a different rj11 cable etc.
Ask again your ISP what settings you need to use.
Try a different modem if you can.