Require Confirmation Email for Account Details Change
I consider the process of contacting customer support to report that an account has been "stolen" too cumbersome. Why not set up the system so that when any account details are changed, a confirmation link will be sent to the registered email address. A user will then have to click on the confirmation link for the new account details to be effected.
Sorry if this is already within you system, but there should not only be a closed loop verification of some sort, but also total across the board provision for MULTIPLE email addresses per account to deal with all the weird real life possibilities of some email account being temporarily or even permanently broken or somehow no longer available.