i have bt internet & phone service & its been fine for years, couple of days ago was on phone when it was crackling then went dead, internet still working. if i plug phone into socket ( no adsl filter )it works but obviously no broadband. with filter no phone service its dead & anyone phoning gets engaged tone. tried new adsl filter but just the same. any suggestions ?
It does sound like a faulty home hub, assuming that is what you are using.
If the phone problem goes away when you unplug the home hub, then a fault within the home hub is short circuiting the phone line, which also appears inside the home hub, to allow the "phone" socket on the back to work.
This type of fault is not unusual.
You will have to report the problem to BT, and explain that it is stopping the phone from working.