There's one thing you didn't think of, and probably what's happening. You're using the same password everywhere, and they got it - somehow. (Your pet's name, your child's name, your spouse/partner's name, your birthday - something common.) From there on, they can change a lot of things on the web that would make you think that they're "controlling" your phone.
First, get a password manager. Use something that someone
can't figure out just by knowing you, something that you know but no one else does, as the password to the password manager. Then make an entry for each of your passworded things - sites, email accounts, VM, apps, etc., and use the password manager to generate a 60 character password (if the thing you're working on won't accept 60 characters, try 50, then 40 - never go below 20; if it can't accept a 20 character password, don't use the app/site/whatever). Change each one, one by one, until anything you've ever put a password on has a randomly-generated password. (Even 20 characters has enough entropy to keep most people from figuring out a collision, but with 60 characters, and a salted SHA256 or SHA512 password, Earth will probably be swallowed up by the sun in its red giant phase before they figure one out.)
Many people here prefer
LastPass Password Manager. I've been using
Keepass2Android Password Safe for so long that I'm more comfortable with it, keeping the data file in a cloud account I have, so all my devices access the same passwords at all times. (LastPass does the same thing for you.)
Then, even if someone
does get one of your passwords, that's all they get - the password for that app or site. And as soon as you see something change, you copy the existing password, save it in the entry for that item, create a new password, and change it. The next time they confidently sign into that whatever, oops, the password no longer works.
But, as belodion said, go to the poice and ask them about filing a report that you're being stalked, even though you haven't identified your stalker yet. Then if anything happens, it's not "he said, she said", you said a long time earlier, and you said it officially. (It costs you a few minutes of your time - either your police/sheriff's department takes complaints like that or they don't. If they do, it takes a few minutes to give them all the information you have [and sign the complaint if you have to]. If they don't, write the situation up, just the way you did here, and give copies to a few different very trusted family members and friends.)
Remember, you can only be walked on if you lie down. Stalkers, like any other type of bully, are basically cowards. When confronted, they flee. (So if an officer of the law eventually identifies your stalker, and just tells him/her that he'd like to talk to them about you, the stalker will need clean underwear.) Don't take it lying down, stand up for yourself.
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