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I think that the problem might be this:
- you need to do the hard reset & data wipe again.
- then immediately after, you need to set the settings for unlocking, for security, for how to log on to the device, in detail and before you restart the device.
- also run a scan to check for the Stagefright exploit in your LG Vista's operating system:
If your phone has (presumably!) the Android OS on it, then if that OS version is not sufficiently updated, then it may contain a significant 'security hole' that allows almost anyone to gain access and control over your phone.
To test as to that security hole, download and use this app:
to tell whether there is such a security hole in your phone's Android operating system.
To avoid the problem in the first place, not just using the Stagefright detector, but also completely updating your Android OS ab initio when you first start using it, is a good idea.
(Some older versions of Android OS cannot be patched, by merely updating that version... but a higher version, if it can run on the older Android OS -compatible phone, can cure that problem.)