Melting and freezing point of water.

First try to differentiate between phenomeon of melting and freezing.

Ice melts while water freezes.

Ice at zero degree has less internal energy than that of water at zero degree. if external energy (equal to latent heat) is given to ice, it melts to water at zero degree. Similarly, if some energy is extracted from water at zero degree, it freezes to ice at zero degree..

So both phenomenon are different and take place in different conditions.