BT rarely get things right. My area was one that won the Race to Infinity. Work was to be complete by March 2012. I'm STILL am unable to upgrade to Fibre Optics!
It's true a remote line check is free, but further investigation has to be paid for. One of the reasons for the check from the master socket is that if the 'further investigation' reveals the fault to be in the house wiring, BT charge the householder (about 120 quid, I believe).