Please see How (Not) To Ask A Question; in particular, it's challenging to debug a parsing script without input data.

In a more general sense, if you use a hash keyed on account number, you can just use that value as an accumulator, i.e.

my %values_hash = ();
while (<inData>) {
    chomp;
    # parse lines
    $values_hash{$ACTNUM} += $value;
}
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or something like that...