Access stateful headless kubernetes externally?

I have created Cassandra stateful/headless cluster on AWS and it's working fine inside the cluster. The only problem is I am not able to access it from outside cluster. I tried most of the things on the Kubernetes documentation or StackOverflow references, but still not able to solve it.

I have a working security group from AWS. Here are my service and statefulset yaml files.

apiVersion: v1
kind: Service
metadata:
  name: cassandra
spec:
  externalTrafficPolicy: Local
  ports:
  - nodePort: 30000
    port: 30000
    protocol: TCP
    targetPort: 9042
  selector:
    app: cassandra
  type: NodePort

apiVersion: "apps/v1"
kind: StatefulSet
metadata:
  name: cassandra
spec:
  serviceName: cassandra
  replicas: 2
  selector:
    matchLabels:
      app: cassandra
  template:
    metadata:
      labels:
        role: cassandra
        app: cassandra
    spec:
      terminationGracePeriodSeconds: 10
      containers:
        - env:
            - name: MAX_HEAP_SIZE
              value: 1024M
            - name: HEAP_NEWSIZE
              value: 1024M
            - name: CASSANDRA_SEEDS
              value: "cassandra-0.cassandra.default.svc.cluster.local"
            - name: CASSANDRA_CLUSTER_NAME
              value: "SetuCassandra"
            - name: CASSANDRA_DC
              value: "DC1-SetuCassandra"
            - name: CASSANDRA_RACK
              value: "Rack1-SetuCassandra"
            - name: CASSANDRA_SEED_PROVIDER
              value: io.k8s.cassandra.KubernetesSeedProvider
            - name: POD_IP
              valueFrom:
                fieldRef:
                  fieldPath: status.podIP
          image: library/cassandra:3.11
          name: cassandra
          volumeMounts:
            - mountPath: /cassandra-storage
              name: cassandra-storage
          ports:
            - containerPort: 9042
              name: cql
  volumeClaimTemplates:
  - metadata:
      name: cassandra-storage
    spec:
      accessModes:
      - ReadWriteOnce
      resources:
        requests:
          storage: 320Gi