I thought we can do a better code (by not using all if's to check the conditions) using modules

No modules needed. Just use logic and nest/chain the if's:

for my $Postpaid_file (@Postpaid_files) {
    open my $POST, $Postpaid_file or die "cannot open $Postpaid_file: 
+$!\n";
    while (my $cdr_post_line = <$POST>) {
        chomp $cdr_post_line;
        my @cdr_post_array = split /\|/, $cdr_post_line;
        if ('Submit' eq $cdr_post_array[9]) {

            if ('GSM' eq $cdr_post_array[12]) {
                $cdr_post_MO_cnt++ if any { /^\Q$cdr_post_array[11]\E$
+/ } @MOresp_error;
                $Total_GSM_attempts++ unless any { /^\Q$cdr_post_array
+[11]\E$/ } @MOresp_error;

                if (any { $_ eq $cdr_post_array[13] } qw( GSM ESMEGW )
+) {
                    $total_MT_P2P++ unless any { /^\Q$cdr_post_array[1
+1]\E$/ } @MOresp_error;
                    $total_MT_P2P_success++ if 'Delivered' eq $cdr_pos
+t_array[7];
                }

            } elsif ('SMPP' eq $cdr_post_array[12] && '0' eq $cdr_post
+_array[10]) {
                $cdr_post_AO_cnt++;   #if any { /^\Q$cdr_post_array[11
+]\E$/ } @MOresp_error;
                $total_AO_success++ unless any { /^\Q$cdr_post_array[1
+1]\E$/ } @MOresp_error;
                $Total_SMPP_attempts++ unless any { /^\Q$cdr_post_arra
+y[11]\E$/ } @MOresp_error;
            }
        }
    }
}
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