If it's dedicated service, you can absolutely cancel. Although the backup solution is offered as an option to your media service, it runs as a separate subscription which you can control through your dashboard.
To cancel, go to your dashboard and cancel the subscription. Please note that if you have not purged your files from the Mozy data center, they will be automatically purged 90 days from your cancellation. This is because if it was a mistake you wouldn't lose anything.