Your problem is that citrus trees are not 'really' deciduous -- they are not meant to lose all their leaves in winter, thus they need light and warmth and so forth 12 months of the year.
Unlike edible figs, which *are* properly deciduous and can be wintered over in a garage or whatnot that stays above freezing, citrus trees need somewhere indoors that does not drop below 50ish, has reasonably good humidity (otherwise: massive spidermite etc problems, and poor tree health), and a very long day of very bright sunny light.
If you have a sunroom or something like that, or a heavily windowed very bright white-walled south-facing room with good humidity, you *can* winter citruses in the house... but it is not easy and often doesn't work well.
Good luck,
Pat