When deleting a process instance (e.g. via RuntimeService#deleteProcessInstance or process instance modification) that was created by a call activity instance, the call activity instance cannot be completed. Not even RuntimeService#signal helps since the call activity behavior cannot be signaled. In consequence, the calling process instance cannot be completed (aside from deleting it).

Solution:

• continue deletion in the calling process instance by applying cancellation propagation as in process instance modification (see https://docs.camunda.org/manual/latest/user-guide/process-engine/process-instance-modification/#cancelation-propagation)