Although I don't want to dive into your personal life, I will say that it would appear as if your Ex might know more about smart phones/devices than you do.. thus latching onto your phones information and even sim card.. and if anyone tells you this isn't possible.. they're prob apposed to the fact that you or I have even brought this up. Just call me "conspiracy theorist".
In my opinion, you need to start from scratch, buy anew smart phone change emails and do not allow anyone to access your devices.. period. Not even your children. Not to sound harsh here and without knowing how old the children are.. kids can be "persuaded" to do things for the other spouse or ex.
In other words.. one email is not enough and staying a head of the game is very important when dealing with a jealous or abusive ex.. Not trying to go Dr Phil on you.. but one really needs to open their eyes to what's around them.
Also, I would switch carriers and or the location as to where you purchased the devices.. seems they could be persuaded by those who might be wanting to track your every move.. Head to a different state or location you've never been before to purchase a new device and service plan. One you've never had before. Do not use the same phone or sim card or even the MicorSD card if one has been mounted.. you need all new devices, service and sim card.
Lastly, do not return to using those apps which could have been tracking you every more on the old phone.. this means giving up that facebook or twitter app etc.. By changing your routine and device should eliminated these possible surveillance techniques.