Not able to receive acknowledgement from ZeroMQ (ØMQ)

Scenario: I am able to send the string typed data from C# to Node.JS app through ZeroMQ (ØMQ) using the following code:
C# push code: 

using (var context = new Context(1))
                {
                    using (Socket client = context.Socket(SocketType.PUSH))
                    {
                        client.Connect("tcp://127.0.0.1:12345");
                        int i = 0;
                        while (true)
                        {
                            string request = i.ToString() + "_Hello_ ";
                            i++;
                            Console.WriteLine("Sending request..." + i.ToString());
                            client.Send(request, Encoding.Unicode); 

                              // <== Here is the issues    
                            string reply = client.Recv(Encoding.Unicode).ToString(); 
                              // <== Here is the issues

                            Console.WriteLine("Received reply :", reply);
                        }
                    }
                }

Node.JS pull code:

pull_socket.bindSync('tcp://127.0.0.1:12345')

pull_socket.on('message', function (data) {
    i++;
    console.log(i.toString() + 'received data:\n');
    console.log(data.toString());
    pull_socket.send('rcvd'); // <== Here is the issues
});

Issue: In C# reply object will contain string "Not supported", but the sent data will be received at Node.js properly.

Question: Can one tell me where I am doing wrong? Please put some light on the issue.

Advanced Thanks

It got solved by using different socket type REQ/REP instead of PUSH/PULL
Following is the code:
C# push code:

using (var context = new Context(1))
                {
                    using (Socket client = context.Socket(SocketType.REQ))
                    {
                        client.Connect("tcp://127.0.0.1:12345");
                        int i = 0;
                        while (true)
                        {
                            string request = i.ToString() + "_Hello_ ";
                            i++;
                            Console.WriteLine("Sending request..." + i.ToString());
                            client.Send(request, Encoding.Unicode); 

                            string reply = client.Recv(Encoding.Unicode).ToString();

                            Console.WriteLine("Received reply :" + reply);
                        }
                    }
                }

Node.JS pull code:

var rep_socket = zmq.socket('rep')
rep_socket.bindSync('tcp://127.0.0.1:12345')

rep_socket.on('message', function (data) {
    i++;
    console.log(i.toString() + 'received data:\n');
    console.log(data.toString());
    pull_socket.send('hello WORLD'); // <== Here is the issues
});

Output on C# console:

Sending request...0
Received reply: hello WORLD