I still receive BT Sport via the aerial - but can only get BT Sport 1, For a while now I get a message on BTSport 2 "This channel is not currently being broadcast". Has BT S2 being turned off via the aeriel now?
Yes. You should've received notification, and the offer of a free Google Chromecast to use to receive BT Sport 1, 2, and ESPN via your broadband connection.
BT Sport 2 on Freeview has now been shut down. BT Sport 1 will go the same way later this year.
It's costing BT money to rent those channels, and more and more people are now streaming BT Sport via broadband. If your exchange is multicast-enabled, and if your line speed is fast enough, you should be able to get sport over broadband. If not, the Chromecast is the only viable alternative.
BT should have contacted you. You need to contact them to find out what is happening.