main.cpp:(.text+0x8f): undefined reference to [object's method]

I have my main.cpp :

#include <boost/thread.hpp>

#include "../headers/BoostUDPSender.h"
#include "../headers/UDPListener.h"
#include "../headers/UDPPacket.h"

using namespace std;

int main(int argc, char** argv) {

        cout << argv[1] << endl;
        cout << argv[2] << endl;

        BoostUDPSender boostUDPSend;
        boostUDPSend.boostUDPPacket(argv[1], argv[2]);
}

and my BoostUDPSender.h

/*
 * BoostUDPSender.h
 *
 *  Created on: 19 Jan 2017
 *      Author: oisin
 */

#ifndef BOOSTUDPSENDER_H_
#define BOOSTUDPSENDER_H_

class BoostUDPSender {
public:
    BoostUDPSender();
    int boostUDPPacket(char* ipStr, char* port);
};

#endif /* BOOSTUDPSENDER_H_ */

and BoostUDPSender.cpp

#include "../headers/BoostUDPSender.h"
#include <string>
#include <iostream>
#include <boost/array.hpp>
#include <boost/asio.hpp>
#include <arpa/inet.h>

using boost::asio::ip::udp;
using namespace boost::asio::ip;

BoostUDPSender::BoostUDPSender() {
}

int boostUDPPacket(char* ipStr, char* port){

      try
      {
        boost::asio::io_service io_service;

        udp::resolver resolver(io_service);
        udp::resolver::query query(udp::v4(), ipStr, port);
        udp::endpoint receiver_endpoint = *resolver.resolve(query);
        udp::socket socket(io_service);
        socket.open(udp::v4());
        boost::array<char, 1> send_buf  = 0;
        socket.send_to(boost::asio::buffer(send_buf), receiver_endpoint);

        boost::array<char, 128> recv_buf;
            udp::endpoint sender_endpoint;
            size_t len = socket.receive_from(
                boost::asio::buffer(recv_buf), sender_endpoint);

            std::cout.write(recv_buf.data(), len);
          }
    catch (std::exception& e)
      {
        std::cerr << e.what() << std::endl;
      }

      return 0;
    }

It all looks fine to me but when I compile with (Other files included below, not relevant to the above):

g++ UDPListener.cpp UDPPacket.cpp BoostUDPSender.cpp main.cpp -o main -lboost_thread -lboost_system -lpthread -std=c++11

I get:

/tmp/ccFPtASO.o: In function `main':
    main.cpp:(.text+0x8f): undefined reference to `BoostUDPSender::boostUDPPacket(char*, char*)'
    collect2: error: ld returned 1 exit status

I don't understand how boostUDPPacket() can be undefined, I'm creating my object and calling the method on it in the conventional way?