Friends ringing in are told we are on pho...

Friends ringing in are told we are on phone or not available, while actually we are in. I tried phone from mobile and BT phone rang only once. Rang BT who told me to remove bottom half of plate and plug in phone to exposed socket, and then repeat with different phone, and then ring myself. Did this and both worked. Well, both gave message re accessing my phone via 1571. Bt sent email but cant find link (was trying /help/checkequip) What next/