Just thought I'd pass on a fix I've just found out.
On Friday my sister called and had to go through call announce when she's got through before with no problem. Having recently renewed my annual line rental I logged into My BT and had a look at phone line extras.
Although I was down for having Caller ID, I went ahead and ordered Caller ID at no cost.
Within the hour I received an email to state that it was setup.
Today my sister rang me and got straight through.
Obviously, BT computer system needs a kick up the provebial when you renew your line rental.