Growing Calla Lilies In Containers
Leaves fall over and get squishy and smell bad.
You may be overwatering your plant.
You need to check the soil before watering. Soil should be moist but not soggy.
Well draining soil with an adequate draining pot is important.
If the bulb has all ready began to rot (the smell may be the biggest clue) it may be best to throw away.
Here are some links with more information.