What can I do about someone who broke into my email account?

My ex broke into an email account I set up for my 7 year old child that was set up by me on an Ipad. They changed the recovery password to theirs, and account password to theirs also without telling or asking me. I created this account for my child he is a minor and so I own the account. I use this to keep in touch with him on his ipad for facetime, etc.

What can I do about this and can I sue that person for this? This is the second time they have done something like this. The first time it was documented in court records that they broke into my personal email and got stuff.

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