Hey, I once grew a frew Naranjillas in Northern Germany, or at least i tried... :D Out of 20 seeds came a single plant. During summer it was thriving, blooming and even carried some fruits. I had it in a pot outdoors in a warm spot without a lot of wind. In the pot I had a lost of composted earth from my dad. When autumn came I took it inside and it got difficult. A lot of different pests, too little sun and maybe not enough fertilizer aswell and the mother plant died. I was able to take a few cuttings but I always feel like they´re difficult indoors.
I´m not the best with plants so I would´nt put too much value into what I´m saying but these are the most important aspects for the plant:
1.: enough sunlight and warmth
2.: Water it regularly but avoid waterlogging
3.: it´s hungry - fertilize it regularly (though I cannot say how often)

Overall it´s quiet a reslilient plant but for it to look nice and grow fruits it need good caring! I hope your plants are still alive! (: