You may be dealing with low light, overwatering, etc. The plant is declining and not happy due to the above issues. It would be best to discard, buy a new plant, and start over.
Here is information on proper care. This plant is easy to grow given average winter-time temperatures and just routine care. Provide bright filtered light in spring summer and fall. During the short day winter months the brightest light include direct sunlight is best. The soil should be allowed to dry somewhat between waterings, but not become bone dry. When good light conditions arrive during the spring and in the summer, fertilize monthly with a soluble houseplant fertilizer.