no matching function for call to vector .. found C++ - c++

Question

I have went over code about 5 times, i am learning c++ and according to me everything should work however that's not happening. Error makes no sense, i mean vector suppose to have "at" function..
I get error:
In function 'void lookup(class vector<Customer,_default_alloc_template<false,0> > &, class string)': findByZipCode.cpp:30: no matching function for call to 'vector<Customer,_default_alloc_template,0> >::at (int)
findByZipCode.cpp
#include <iostream>
#include <string>
#include <fstream>
#include <vector>
#include "customer.h"
using namespace std;
Name readRestOfName(istream &in,string f) {
string g;
getline(in,g);
Name abc (g,f);
return abc;
}
Address readAddress(istream &in) {
string street, city, state, zip;
getline(in, street);
getline(in, city);
getline(in, state);
getline(in, zip);
Address abc (street, city, state, zip);
return abc;
}
void lookup(vector<Customer>& v, string zip) {
// COMPLETE
vector <int> matches;
cout<<v.at(2).getName()<<endl; <<<---------------error here!!!
}
int main() {
// open customerdata file
ifstream in("customerdata");
vector<Customer> v;
string f;
while (getline(in,f)) {
Name n = readRestOfName(in,f);
Address a = readAddress(in);
Customer abc(n,a);
v.push_back(abc);
}
in.close();
string zip;
while(!cin.fail()){
cin>>zip;
lookup(v,zip);
}
return 0;
}
customer.cpp and customer.h
.cpp
#include <iostream>
#include "customer.h"
#include <string>
using namespace std;
string Customer::getName() {return n.getFamily() + ", " + n.getGiven();}
string Customer::getAddress() {return a.getStreet() + " " + a.getCity() + " "+ a.getState()+" "+a.getZip();}
string Customer::getZip() {return a.getZip();}
.h
#ifndef CUSTOMER_H
#define CUSTOMER_H
#include <string>
#include <iostream>
#include "name.h"
#include "address.h"
class Customer {
private:
Name n;
Address a;
public:
Customer(Name b,Address c): n(b), a(c) {}
std::string getName();
std::string getAddress();
std::string getZip();
};
#endif