This was one of WhatsApp’s most anticipated feature rolled out few weeks ago… unfortunately, the recall feature isn’t as reliable as it looks.
Last month, WhatsApp introduced a 'delete for everyone'feature, allowing users to unsend an embarrassing message within seven minutes of sending it. The message once deleted from the senders end’ automatically delete the message from the receivers end too.
But a new report from a Spanish blogclaims that WhatsApp messages that are deleted are actually still on the device, and can easily be accessed through Settings by the recipient. The recipient can easily access the deleted messages regardless whether it has been deleted from sender's end.
Whenever a notification comes in to an Android devices, it is stored in the notification log – whether or not it is subsequently deleted by the sender.
While the bulk of the data in the log is technical information, the first 100 characters of the notification message is also recorded.

So while users may not be able to see the message within WhatsApp after it is deleted, they can still see it in the notification log – which can be accessed in two ways.
How to Access Deleted WhatsApp Messages
Method ONE:

The trick currently only works onAndroid 7.0.
Firstly, users can create a home screen Settings widget:
1) Press and hold home screen
2) Press widgets icon
3) Scroll down to Settings
4) Drag and drop onto home screen
5) Click on widget
6) Scroll down and click on the notification log
Click on the message you want to see
Method TWO:
1. Download notification history from appstore here
2. Search the message in the Android notification log.
However, the first 100 characters of the message will appear in the line starting with'android.text.'
Users will only be able to view thefirst 100 characters of deleted messages, and the notification log will clear every few hours, or any time the device is restarted.

This raised a serious security issues with WhatsApp since one of the main reasons people use WhatsApp over text messaging is that it uses end-to-end encryption, that is seen as a secure option.

Cc; Lalasticlala,mynd44,honsule, dragnet, puskin

I have lost files by accident many times, and I have conclusion of how to restore deleted files like whatsapp messages on my account.
You can always upload the messages to have a backup files, when you delete the messages by mistake, just import the messages.
In addition, you can try recovery software to recover, it is also possible.