Registered my iPhone on my ex's Mac and now I have a ton of overages When I first got my iPhone 6+, I registered it on my now exhusbands MacBook. Since the divorce and the separation of accounts, I still have horrible "gaming" data overages. I've never played a game on my phone. I have no games downloaded. He has also stolen money from my credit card once I used it on my phone. 

Does this mean he is still accessing it? I have changed my number and my Apple Id. (the password reverted back though). All the "usage" is done in the wee hours of the morning when im not even on my phone. Can he be causing it?
Probably not, considering there is no way to access your plan or wireless service from a macbook, you shouldn't have to worry about that.

I would check the settings (view and adjust data use https://support.apple.com/en-us/HT201299) on your phone and ensure that someone isn't swiping it when you are not around and playing games (like some smart kids.)

If that doesn't fix the problem I would recommend calling your phone provider and investigating, someone else may have access to your plan via calling up your service provider and adding additional phones, or you may be billed on accident.