If you are currently living abroad, but spent some time living, working or studying in the Netherlands, you should have taken out health insurance at the time. Since you neglected to do this, you now have to pay a fine.
You can file an objection to the fine by sending a letter to the Central Administration Office (CAK). You must do so within six weeks of having received the fine from the CAK. For more information, visit the CAK website.
You do not need to put a stamp on the envelope.
If you are filing an objection, you are still required to pay the fine. If your objection is upheld, you will have your money refunded.