Your prose description of what you think your code does sounds nice. But it does not relate at all to what your program is doing, otherwise your program would be working.

Reduce your program to a small, self-contained example. Also post the input data. Maybe your input data is nothing at all like what you expect. The Data::Dumper output seems to confirm that. The unusual length of 8 bytes for what should be a 4-byte number confirms that. So investigate, reduce and debug your program and thus your problem.