Am I being screwed by the garage?

Hi everyone, I just want to see if I'm being screwed around or not. My car's engine/drive train broke down (BMW 520d GT) in Scotland and I'm in the midlands so I can only contact them through the phone.
I had it towed to the only place available in aberdeen that said they could fix this, they diagnosed it to be the engines fault and told me it could run but not for very long with a new starter motor and a new turbo. Now they have changed both they're telling me neither of those repairs worked and I need a new engine... have they just charged me over £1k in useless repairs? If so is there anything I can do? Thanks.
TDLR; Garage told me I need new starter motor and turbo, after the change they said it didn't work and need a new engine.