I would like to create bot in whatsapp. The Idea is here when a user sends a whatsapp message to my phone number that should reply to them.
I have researched twillio since it's like a sandbox twillio uses it own whatsapp number and So when a new user comes the user should send the sandbox number. Then I searched for whatsapp API I don't have any company or anything so there I can't use the official whatsapp API.
Is there some other way of using whatsapp API when I recieve a message it should reply immediately.
Unfortunately, since WhatsApp is only opening its APIs to its trusted/business partners, you can only access it using their services. Some of the examples includes,

Vonage
Infobip
Wati
Twilio as you mentioned

If these are not enough for you, you can always write your own bot in Python using selenium to scrape the web app for WhatsApp and listen to new message by checking the page regularly.
How to create a whatsapp bot?