Account problem

Why did you let someone use your account ? He doesn't sound like much of a friend if he's given access to it to other people and continues to use it after you asked him to stop. You could consider using two-factor authentication on the account : Two-factor authentication for Apple ID - Apple Support . And see if you can remove devices from the account on http://www.appleid.apple.com : Check your Apple ID device list to see where you're signed in - Apple Support

For wifi, you've tried rebooting both the router and the phone ?

If you are using two-factor authentication nobody should be able to change its password without the verification code that is sent to a trusted device.

If you want to get the account (and therefore all of its past purchases) deleted try : https://privacy.apple.com/

You can create a new account with a new email address.

If you delete your account, you lose all access to previous purchases. I suggest you use the different email address to make a name change to your current account. That will allow you to retain access to your purchases.

Apple ID Name Change

What to do after you change your Apple ID or password - Apple Support I suggest doing this before you change your Apple ID or password.