Γεια σου Ιάκοβε
The correct way to say 202, 203 is "διακόσια δύο", "διακόσια τρία". You could say "δύο μηδέν δύο", "δύο μηδέν τρία", but it is not used for small numbers.
διακόσια δύο, τριακόσια δύο is nominative
διακοσίων δύο, τριακοσίων τριών is genitive. When you refer to the number of a hotel room you always use nominative.
Example:
Το κλειδί του δωματίου διακόσια δύο χάθηκε = The key of the room two hundred and two was lost.
But: Η ζωή διακοσίων δύο ανθρώπων είναι σε κίνδυνο. = The life of two hundred and two people is in danger.
As for the ν sound in the ending of διακοσίων, τριακοσίων and other numbers, is not ignored when we speak.
