Address passed by reference changes after function completes [duplicate]

Question

The task is to read comma separated values in a dynamically allocated array of structs. The reading part works well, but after completion of readcsv() the reference to *addr changes address from 0x55555555a6e0 to 0x1000. Not exactly what I'm looking for since I'll have to sort and print this array afterwards. How do I prevent this from happening? Have I overlooked something in terms of scope?

#include <stdio.h>
#include <stdlib.h>

#define LEN 20

struct address {
    char *fname;
    char *lname;
    long postcode;
    char *city;
}; 

typedef struct address ADR;

int addr_count(FILE *file) {
    fseek(file, 0L, SEEK_END);
    long file_size = ftell(file);
    fseek(file, 0L, SEEK_SET);

    char *buff = malloc(file_size);
    int c = 0;

    while(!feof(file)) {
        size_t res = fread(buff, 1, file_size, file);

        for(int i = 0; i < res; i++) {
            if (buff[i] == '\n') {
                c++;
            }   
        }
    }

    fseek(file, 0L, SEEK_SET);
    free(buff);

    return c;
}

int readcsv(const char *filename, ADR *addr, int *naddr) {
    FILE *file = fopen(filename, "r");

    if(file == NULL) {
        printf("Error: couldn't read file\n");
        return -1;
    }

    *naddr = addr_count(file);
    addr = malloc(sizeof(ADR) * (*naddr));

    if(addr == NULL) {
        printf("Error: out of memory.\n");
        return -1;
    }

    ADR *start = addr;
    fscanf(file, "%*[^\n]\n");

    for(int i = 0; i < *naddr; i++) {
        addr->fname = malloc(sizeof(char) * LEN);
        addr->lname = malloc(sizeof(char) * LEN);
        addr->city = malloc(sizeof(char) * LEN);
        
        fscanf(file, "%[^;];%[^;];%ld;%s\n", addr->fname, addr->lname, &addr->postcode, addr->city);
        addr++;
    }
    addr = start;

    fclose(file);

    return 0;
}

int main() {
    ADR *addr;
    int naddr;

    readcsv("addresses.csv", addr, &naddr);

    free(addr);

    return 0;
}