Hi vineet09,
The kind of phone you're looking for is slowly moving towards obsolescence. You won't find those kind of phones in a couple of years as all brands are competing for the smartphone race. Even if you do buy such a phone, it would probably be old stock or will not be getting support for hardware issues in the future. I recommend that you give your father a simple starter android so that he can get better acquainted with touchscreen devices, just like I helped my dad with the Moto G.
But if you still want a alphanumeric phone with whatsapp, you could try the Nokia series 30 phones. Nokia is known for superior battery backup and durability, hence it should be a good match to your requirements. If not available locally, try some online stores, they seem to have stock.
