Help and advice needed land rover 4

I have a land rover 4 , just hit 15000 miles ... I don't drive on the motorway . Car was bought brand new from dealer . Car started to rattle , I called ranger over assistance , they took car away and said huge problem with engine .
I got called today ... Every though warning light for oil never came on they said the engine is totally screwed worst way is £19000 .. Oil was almost empty.
Obviously I said its madness .
They told me they want the loan car back .
Has anyone actually seem a oil warning light come up on the dash ? Do they exist ...
Car should be serviced every year or 15000 miles ... I just hot 15000 so was going to take In end of jam but as I didn't I'm not in warranty ...
Apparently a car that does 15000 miles shouldn't drain totally of oil and they said no oil leak ..
Any advice .. Tia