The most likely explanation is that one of the 2 wires of your phone line is broken - voice needs both wires but ADSL with (sort of) work with only 1 (& I've temporarily forgotten what the technical term for this is).
The best course of action is to report it to BT (or whoever you pay the line rental to) as a voice
fault (don't mention broadband at all - that may just confuse things). Getting the voice fault fixed should sort the ADSL out too.
"If I have not seen as far as others, it is because giants were standing on my shoulders."