Was this BT? If so, I am not surprised. There are a number of exchange
and line faults, which come and go for very little apparent reason.
Whenever we see the BT van in our area, we anticipate another faulty
telephone incident. As someone has said, it is quite common to have a
line which does not clear down properly, particularly if there is a lot
of rain around. Unfortunately BT does not now have the engineering
capacity or expertise at local level to properly investigate exchange
faults. We have a peculiar modem problem with dial up, which appears to
be related to the BT automatic line attenuation level setting, but there
is absolutely no interest in actually finding out what causes the
problem. Hopefully your problem will be simply related to local
engineering works and will not recur until the van is in your area again!

Regards
Capitol