@peuga
It took a while, like half a decade or so, for DHCP to settle.
Stuff like PPPoE was invented, just after PPP, to do simple things way more complicated.
The thing is : it should be as easy as this :
6c66ec9e-755c-478e-ac0b-a6716e52a3e4-image.png
and some minor DHCP6 Client (WAN side) settings :
9d9a4aba-a075-4906-a584-4dd184c6f750-image.png
and when the ISP (or upstream ISP router) is 'IPv6 aware and plays by the rules) you can now start "tracking" IPv6 on LAN(s) :
77ef97ca-a7c4-45b4-ac6f-7400af1fd4ec-image.png
The reality is different.
Very few ISPs know what IPv6 is - everybody is reading the RFC, and (neraly) nobody understood them.
You said : "I've called them" : that's not even possible anymore here in Europe ^^ If you don't know what networking with IPv6 and they don't know neither, then .... well, IPv4 will still work just fine.
Btw : it might work over PPPoE, but the last time I used PPPoE is 'decades' away now.