TypeError: no implicit conversion of Symbol into Integer

Your item variable holds Array instance (in [hash_key, hash_value] format), so it doesn’t expect Symbol in [] method.

This is how you could do it using Hash#each:

def format(hash)
  output = Hash.new
  hash.each do |key, value|
    output[key] = cleanup(value)
  end
  output
end

or, without this:

def format(hash)
  output = hash.dup
  output[:company_name] = cleanup(output[:company_name])
  output[:street] = cleanup(output[:street])
  output
end