Remove Call of Duty (Activision) account Completly

impossible

'There is no way to close or shut down an account.' 

This answer is for an Advanced user. Please do not attempt the below solution if you are not comfortable editing the Registry. Damaging the Registry could result in very adverse effects to your system. USE AT YOUR OWN RISK. We recommend that you backup your system registry before making any changes.  To create a backup of the registry do the following: Click Start button > Run (select the search box if you are using Windows Vista) At the prompt type: REGEDIT. The registry editor will open. Select File -> Export Save the file in an easy to get to location (like the c:\ drive) Name it something like RegBackup Make sure the export range is set to "all" at the bottom Click on Save First it will be necessary to remove the registry keys the game creates. Please be cautious when working with the registry as it is very sensitive. Deleting the wrong thing can result in complete operating system failure. Click Start button > Run. At the prompt type: REGEDIT. The registry editor will open. Click the "+" next to HKEY_LOCAL_MACHINE. Click the "+" next to SOFTWARE. Click the "+" next to ACTIVISION. Right-click on the CALL OF DUTY folder and select Delete. Close the registry editor. Once the registry keys are removed, we'll need to remove the game files from your hard drive. These instructions assume you've installed the game in the default directory. Double-click the My Computer icon. Double-click the C:\ drive. Double-click Program Files. Right-click on the Call of Duty folder and select Delete. Remove the COD.INI file from your hard drive. Click the Start button > Find (or Search) > Files & Folders. Search your C:\ drive for a file named COD.INI. The file should be located in C:\WINDOWS. Delete this file. Reboot your machine. At this point the game is completely removed from your system.