Yeah its the same for me I already raised it earlier today but I'm guessing no one will be that interested as sadly its usually yahoo issues. Whilst BT/yahoo email starts off with the BT front end its still essentially the yahoo system. I use webmail and web calendar so if its from a server access and it may be a different issue. Hopefully someone might poke the BT people on here as its still down on the web versions. It does give some output on chrome for Pc but its not really workable and its very confused almost like there is an update been done but its trashed the system.
Of course you could ring up or report a fault on the front end system but i'm not sure anyone at the triage stage will know what it is and to be fair its not really a BT system if as I say its the yahoo version of BT mail.
I did not receive any response from BT re the issues and I did not have the time to raise with them via a phone call, but clearly BT recognised there was a problem even though it was not reported on the service pages. My calendar was fixed and working 24 hours after the problem was first noticed.