I imagine they are not being fertilised. Try using a small paint brush and brush pollen from one flower to another.

These plants love hot weather. They won't perform well at all if it's too cold. You are just at the threshold of what this plant will tolerate. These are members of the nightshade family. Anything below 50°F - they are stressed. The ideal temperature is between 27 and 32 degrees C and it is important that this temperature does not fluctuate too much, especially night time temperatures. You may be better off growing them in a hot house.

If indoors, as it looks, be sure it gets plenty of light, as well as pollination, and keep the room on the warm side--above 24º C.

Thank you to all that replied. I will try what you have suggested.