Even using this app i am getting the contacts back into my androud after a day or so
Just login to your Google account and delete all that you don't want
Just select individually or everything
It's your choice
I think you took a backup of all your contacts somewhere either in your SD Card or in the phone memory. That is why your phone is able to get back the contacts even when once deleted. So check that also once.
Usually taking backup of contacts on the SIM card is useful so that when you change your phone's you can easily transfer them.
Even taking backup via cloud is useful in case you loose your phone.
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