public function pause()
    {
        $this->status('paused');
        $started = $this->subscriptionStarted();

        if (!isset($this->subscriptionPlans[$plan = $this->plan()])) {
            $this->delete();
            throw new BillingSubscriptionPlanException(sprintf('Your %s plan is not exists in our website'));
        }

        $endTime = $this->findTimestampOfSubscription($started, $plan);
        $left = $endTime - $started;
        $this->subscription_paused_left = $left;
        return $this;
    }