Hi,
As we are a startup firm, employees here are not use to work in deadlines and usually skip due dates or modify them regularly till task closure.
You are requested to help me with any feature asana have which provide notification on every due date modification “or” the way to freeze due date.
Thanks…
Welcome 
According to Email notifications from Asana | Product guide • Asana Product Guide you can get a notification if a task assigned to you has its due date changed. If the task is not assigned to you, you won’t.
I can see two solutions:
#1 Educate users. That would be the best obviously but the hardest.
#2 Develop a code using the API to watch for due date changes on certain tasks and notify whoever needs to be notified (maybe the manager given in a custom fields on this task).
However there is a third solution apparently 
. According to Creating task dependencies | Product guide • Asana Product Guide if a task you depend on has its due date changed, you get on notification. So you could have a master task, depending on several other tasks, and you would get notifications if one them has its due date changed. Voilà!
Welcome, As a side note I train my clients (per GTD the best way to make sure dated stuff gets done) never to put a due date on a task only if you must do the task (not want to) on a certain date… i.e. pay bill Monday, since it’s due, the ones that they want to do today we call “ASAP Tasks” both are marked for today (TAB Y) unless it’s for a later date it’s Upcoming (TAB U).
Consequently the chances of finishing daily the dated tasks are much higher, since they know all these tasks must be done today and when they finish the dated tasks they start one by one on the non dated ASAP tasks…
Hi @ruchi and welcome to the Forum!
@Bastien_Siebman and @Leiby_Markowitz both shared some great and helpful tips! Let us know how you have aditional questions 
Have a great day!