Other Monks have already provided you with the answer to your problem. However, it might save you a little typing and also save entries in the symbol table if you set up your $ref_HoH directly using the curly brace anonymous hash constructor, like this

my $ref_HoH = 
{
11 => {
         4 => 'Four',
      },
33 => {
         1 => 'One',
      },
2 =>  {
         2 => 'Two',
      },
};
[download]

Note also that you don't need to quote your hash keys (unless they contain spaces) when using the => (fat comma).

Cheers,

JohnGG