later I heard that 777 pilots do not practise ditching on their simulators, is this correct?
Not entirely. Ditching has never - to my recollection - been included in any manufacturers recommended training programs. However, I am aware of several airlines which included such training following the Sullenberger experience.
That said, ditching in an Airliner is an
extremely unlikely event to occur.
In fact, "Sully" probably got the Staticstical "...one in whatever many..." for the remaining century!
Cheers