The only way I know of to get rid of a stuck call (presuming a restart of Interaction Desktop does not get rid of it) is to restart the TSServer subsystem on the IC Server (or reboot the server, which restarts everything).
A stuck call is a symptom of a bug in TSServer. If you are not running the latest version of IC, update your system to make sure you have the latest patches.
If you are running the latest version, contact Support.