I think use warnings; and use strict; would go a long way toward solving this for you. You call your arrayref $user sometimes, and some of those may be in the code.

The last index of $users will be in $#$users, not $$#users. Observe,

$ perl -Mstrict -we'my $foo = ["a".."z"];print $#$foo,$/'
25
$ perl -Mstrict -we'my $foo = ["a".."z"];print $$#foo,$/'
14354
$
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I'm leery of your hash keyed to surname. When you insert Minnie, Mickey will get clobbered.