Someone finally answered the phone after the second outage tonight.
As I was told it was happening back in September, they see no need to tell users that their connection would go down when they implement CGNAT.
Their network team apparently decide on the day which sites to do that evening.
They have really gone down hill. You used to be able to talk to someone technical when you called. All you get now are call handlers.
Views expressed are mine and not necessarily those of my employer.