Yes, same situation in The Netherlands with KPN (XS4ALL, Telfort etc.).
Sophos really needs to implement this feature and don't forget PPPoE support.
We have reached the point DHCPv6 Prefix Delegation is an essential feature and a simple requirement. It's almost 2019. The largest ISP in my country requires DHCPv6-PD over PPPoE.
"Take my money" and implement this feature please so that we can get rid of pfSense.
Please combine this with DHCPv6-PD.