code: func (c *CallService) Cancel(sid string) (*Call, error) {
  	data := url.Values{}
  	data.Set("Status", string(StatusCanceled))
  	return c.Update(context.Background(), sid, data)
  }
docs: // Cancel an in-progress Call with the given sid. Cancel will not affect
  // in-progress Calls, only those in queued or ringing.