Where is My Mail App!! and why does MS call my phone log in attempts as suspicious??

[Windows Central Question]

for the past couple of weeks, something weird is happening to my Lumia 520, the default Mail app is Missing! it's not there in my App List and i cant search for it in store of course.
Also, i cannot access my phone contacts through the 'People' app since that crashes the moment it launches. same with the One Drive App.
Called up Windows Phone Chat Support but they couldn't figure it out either!!
Hard resetting the phone has worked once but within a day the issue returned!