Saul, which Luna model is it? Are they the same strings that came with the guitar? Have you changed them recently? I mean, old strings will sometimes be hard to get in tune.

What's the intonation like up the neck: i.e. is each open string in tune when you sound its octave at the 12th fret?

If there is indeed a fundamental intonation problem and the guitar is indeed untunable, can you adjust the truss road?

I would take it to a luthier and at least find out what the problem is, if only to satisfy your curiosity Get a quote to fix it. It might not be very much money. I wouldn't be too sure it'll cost more than the guitar's worth - looking online all the Lunas I can see cost over £120 new. It might only be a £30 job to get whatever the problem is fixed.