By the way, if your line drops when the phone rings that does point bad house wiring and/or bad DSL filters, which is so is going to make your ADSL unreliable and slower than it should be.... worth getting BT to rewire your phone sockets and master socket unless you are absolutely confident it is all tip top. However it sounds like you have an ADSL 'long line' ... and these are slightly different beasts to regular ADSL, and you can sometimes ask to have your line fixed at 2Mbps or slower for improved reliability.
A house a third a mile away from me in my village off the same cabinet and main wiring loom has the same as you... 1.5 To 2 Mbps, unreliable, and disconnection with phone ringing and told not much BT can do to improve, and I get 3.8Mbps ... fairly rock solid other than ionospheric noise which one can do nothing about unless change planet... but I had BT re do my wiring my side of the master socket demarcation and put a new master socket/master ADSL socket in with a primary filter... So who ever advised not likely to improve you should qualify their advice and ask how they tested your house wiring... a lot of mis information on xDSL... it actually get quite technical and equally reliant on domestic wiring that the house holder is responsible for.
Again for mobile have you checked all networks and considered and/or roaming sims/or mobile home repeater (though check approved for connection to your network such as Cel-fi) with an antenna mounted high in your house? The best networks to try are O2 and Vodaphone as they use the lower GSM 850/900MHz band and that is better for longer distance and less attenuated. IT in the country side can be quite different from what the townies and suburbanites are used too... it sometimes need looking a bit below the covers to get it to work for you... I end up giving a fair amount of advice around where I live on this..but of course there are some genuine complete 'not spots' ... and then Satellite is your friend ... that is universal across the U.K.