Your "Calla" is most likely a Zantedeschia, which is used as a pot plant, whereas Calla (Calla Palustris) is found in ponds and water gardens. That's just a bit of background.
The Zantedeschia flowers into the summer and then retracts its leaves. Coming from Ethiopia, it stops growing in the summer, a lot like our tulips. Your plant has now produced pollen. Assuming you don't want any pollen from them to grow new plants with, it is recommended that you remove the seed stems when they appear. The "Calla" should put its energy into the rhizome, from which it will produce shoots next year.
For this to happen, you need to cut off the seed stems and care for the Zantedeschia as follows: Leave the plant outside until the autumn, keeping it relatively dry without allowing the rhizome to dry out completely. Make sure it gets a bit of water every now and then. Before the start of winter, put the plant in fresh, mineral-rich potting soil. Over the winter period, keep the plant at a cool temperature, around 5 degrees. Then, from the middle/end of January, put it somewhere very light and around 15 degrees warmer. Encourage shoots by slowly increasing the amount of water as required. Start fertilising when the greenery has reached a hand's width in height, and do so gradually. Then, at the end of the flowering period, stop fertilising the plant and slowly reduce the amount of water you give the plant. This is the cycle you need to follow to successfully care for your "Calla" plant.