I transplanted a Calla Lily and all the stems, including all the ones with flowers, once they get to a certain height, droop and
die. New stems with leaves keep coming up, but as soon as they get to that height the same thing happens.
Certified GKH Gardening Expert
It is, more than likely, being overwatered. This will be the most common cause of the symptoms that you are experiencing. This article will help you to water calla lilies: https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/calla-lily-watering.htm