The first thing that I'm seeing looking at your code snippets is that you confuse array elements and array slices. You write:

push(@{@{@holder[$sheet]}[$iC]},@{@{@data[$sheet]}[$iC]}[$index]);
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and I'm almost certain that you mean:

push(@{${$holder[$sheet]}[$iC]},${${$data[$sheet]}[$iC]}[$index]);
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To simplify - to access an array element you use:

$array[254] = 'foo';
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The @array[...] notation is used to access a slice, for example @foo = @array[2 .. 4]; which would copy the data from $array[2], $array[3] and $array[4] to $foo[0], $foo[1], $foo[2].

Fix your code to use $ instead of @ correctly, and see if that fixes your problem.

Michael