To use a country's AppStore, you must
1] be in that country;
2] have a credit/debit card issued by a financial institution in that country; and
3] have a verified billing address in that country.
Suggest you contact the developer of whatsapp and ask him to allow its
sale in your country's AppStore. There are countries where the government
blocks the sale and use of certain apps; is that the case where your are?