Trello has never notified me about a deadline but the push notifications is activated in my android.
It sounds like you might not be watching the card in question. In order to receive notifications for many of the actions that happen on cards, you'll first need to watch the card.
https://help.trello.com/article/799-watching-cards-lists-and-boards
Can you give that a try with a new due date set? That should get the push notification sent to you.
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