It is very unfortunate if you are in a location where you can't get the TV aerial versions, can't get the Infinity multicast versions, and can't get the ADSL multicast versions. The other option you could try is to set up a Freesat from Sky box/card and order them on that.
See this post from yesterday by someone else with the TV reception issue.
The 80 main transmitters cover most of the UK and BT can't force their commercial channels to be put on the additional relay transmitters that don't transmit the full set of multiplexes.
Salcombe - lovely place to live but unfortunately you are 'in the sticks' when it comes to technology. None of the relay transmitters in your area will transmit the commercial multiplex that carries BT Sport, and because of Geography you can't pick up the main transmitters at Beacon or Caradon Hill.
If you were living in Cornwall you might have been lucky enough to have Infinity by now, but I have no idea when it's likely to reach small towns in Devon.
So yes, your only options are to watch via the webstream, or else get a Freesat from Sky box & dish installed.