Correct, general speaking, you can claim back the half month salary. However, that has to depend on what terms and conditions you had signed in your employment contract and the acknowledgement letter you signed regarding your last day.
I suggest you call the labour department to further clarify your case (2717 1771).
If you have the time, why not. You can always drop the case anytime by giving them notice. At the meantime, labour department will issue a letter to your ex-employer asking them for more supporting details.