Structures saved every second index value in C - c

Question

I'm writing a project and have stumbled upon a problem.
My part has to take the entries and save them as a structure into the file. Everything seems to work properly until I try to save them. That's my get_db_entry code:
printf("Please enter a forename: ");
fflush(stdin);
fgets(st[index].forename, STRING_SIZE, stdin);
printf("Please enter a surname: ");
fflush(stdin);
fgets(st[index].surname, STRING_SIZE, stdin);
printf("Please enter an address: ");
fflush(stdin);
fgets(st[index].address, STRING_SIZE, stdin);
printf("Please enter plate number: ");
fflush(stdin);
fgets(st[index].plate_number, STRING_SIZE, stdin);
printf("Please enter account balance: ");
fflush(stdin);
scanf("%f", &st[index].balance);
And saving looks like this:
void save_db(struct customer *st){
FILE *pFile;
int file_nof=0;
FILE *pnof;
pnof=fopen("nof_db.dat", "rb");
fread(&file_nof, sizeof(int), 1, pnof);
fclose(pnof);
printf("File_nof value: %d\n", file_nof);
fflush(stdin);
if((pFile = fopen("database.dat", "ab")) != NULL) // Open file in write/update mode
{
fwrite(st, file_nof*sizeof(struct customer), 1, pFile);
fclose(pFile);
}
else
{
printf("Cannot open file");
exit(1);
}}
I've checked numerous times and the index value is being passed on correctly, meaning that it counts 0,1,2,etc.
The entries are being saved for 0,2,4,6, so there is literally a padding by an empty structure every entry, say: index=0 always saves properly, then index=1 - empty, though the program saves into index=2 automatically.
This leaves me with empty spaces and a waste of space.
There are multiple checks along the way that check the value of "index", so I've no idea what's going on.
PS.
file_nof = nof_entries = index+1