The Nokia OVI Store was replaced by the Opera Mobile Store in the first quarter of 2015. If you are using an S40 device, you can download WhatsApp from there. However, we strongly recommend that you download WhatsApp from our website, where we always have the latest version of WhatsApp.
We will continue supporting Nokia S40 for the foreseeable future. You can check our FAQ page and learn how to update WhatsApp on your Nokia S40 phone.
Cheers,
WhatsApp Support Team