Error munmap_chunk(): Invalid Pointer C programming Dynamic Memory Allocation

Question

Unable to figure out this issue that is causing my program to throw this error, i'm reading from 3 files and have to make a dynamic array to store all the values of the text file(which are INTs). Then sort and print out to a new file.

This is my updated code

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

//Jeffrey Hennen

int cmpfunc (const void * a, const void * b)
{
   return ( *(int*)a - *(int*)b );
}

void main(){
     //printf("hello\n");
     int counter = 0;     

     FILE *fp;
     fp = fopen("list0.txt", "r");

     int ch;
     while((ch = fgetc(fp)) != EOF){
          //counter++;         
          if(ch == '\n'){
              counter++;
          }
     }
     //printf("%d\n", counter);
     //printf("hello1\n");

     fclose(fp);
     fp = fopen("list1.txt", "r");     

     while((ch = fgetc(fp)) != EOF){

          //counter++;        
          if(ch == '\n'){
              counter++;
          }
     }
     //printf("%d\n", counter);
     //printf("hello1\n");
     fclose(fp);
     fp = fopen("list2.txt", "r");

     while((ch = fgetc(fp)) != EOF){
          //counter++;          
          if(ch == '\n'){
              counter++;
          }
     }
     //printf("%d\n", counter);
     fclose(fp);
     //printf("hello2\n");
     int size = counter;
     int * sizeOfFile = (int*) malloc(size * sizeof(int));

     //int z = 0;
     //for (z = 1; z<= size; z++){
     //     printf("%d %d\n", z, sizeOfFile[z]);
     //}

     char ch1[sizeof(int)];
     int counter1 = 0;
     int y = 0;
     fp = fopen("list0.txt", "r");
     while ((ch = fgetc(fp)) != EOF){
          fgets(ch1, sizeof(int), fp);
          y = atoi(ch1);
          printf("%s\n", ch1);
          sizeOfFile[counter1] =  y;
          counter1++;
     }
     fclose(fp);

     fp = fopen("list1.txt", "r");
     while ((ch = fgetc(fp)) != EOF){
          fgets(ch1, sizeof(int), fp);
          y = atoi(ch1);
          printf("%s\n", ch1);
          sizeOfFile[counter1] =  y;
          counter1++;
     }   
     fclose(fp);  

     fp = fopen("list1.txt", "r");
     while ((ch = fgetc(fp)) != EOF){
          fgets(ch1, sizeof(int), fp);
          y = atoi(ch1);
          printf("%s\n", ch1);
          sizeOfFile[counter1] =  y;
          counter1++;
     }  
     fclose(fp);

     qsort(sizeOfFile, size, sizeof(int), cmpfunc);
     fp = fopen("Hw3.out", "w");  
     int x = 0;   
     for(x; x < size; x = x + 1){
          fprintf(fp, "%d\n", sizeOfFile[x]);         
     }
     fclose(fp);

     free(sizeOfFile);


}