Collect2: error reference method without defining - c++14

Question

I'm building a basic program to make a list that consists of objects in c++, I've looked over the code several times and am just stuck, my professor isn't answering and have to turn this in soon, if anyone can help me find why it's saying that getTotal2020() is not defined when clearly it is. I am compiling with all the files and the #include is in all the files as well.
I've tried different ways of accessing this method but every time it throws errors. At least how I have the code now, I don't have any errors.
class Data {
public:
Data(string neighborhood, int total2020, int numOfMen, int numOfWomen);
string neighborhood;
int total2020;
int numOfMen;
int numOfWomen;
~Data();
string getNeighborhood();
int getTotal2020();
int getNumOfMen();
int getNumOfWomen();
};
Data::Data(string neighborhood, int total2020, int numOfMen, int numOfWomen) {
this->neighborhood;
this->total2020;
this->numOfMen;
this->numOfWomen;
}
string getNeighborhood(string neighborhood){
return neighborhood;
}
int getTotal2020(int total2020){
return total2020;
}
int getNumMen(int numOfMen){
return numOfMen;
}
int getNumOfWomen(int numOfWomen){
return numOfWomen;
}
class Node{
public:
Node* next;
Data* data;
Node(Node* next, Data* data){
this->next = next;
this->data = data;
}
Node* getNode(){
return next;
}
Data* getData(){
return data;
}
};
void List::findElement(int findMinPop){
Node* aux;
aux = head;
while(aux){
if(aux->getData()->getTotal2020() >= findMinPop){
cout << "The population is greater" << endl;
} else {
cout << "The populations is less than you were looking for" << endl;
}
aux = aux->next;
}
}
The error is gives me is:
/tmp/ccJeheba.o:main.cpp:(.text+0x3ed): referencia a `Data::getTotal2020()' sin definir (that the method is not defined)
/tmp/ccJeheba.o:main.cpp:(.text+0x3ed): reubicación truncada para ajustar: R_X86_64_PC32 contra el símbolo `Data::getTotal2020()' sin definir
collect2: error: ld devolvió el estado de salida 1