Unfortunately, there's not an Instagram bot service available at this time that is 100% compliant with Instagram.
In other words, you run the risk of getting your profile shut down when you use any bot platforms.
The only legitimate platforms we know of at this time are ManyChat and Chatfuel, which are going through a private beta for Instagram bots (that we're currently participating in.)
They don't have a public release date yet, but I would guess sometime next year any business will be able to apply and use an Instagram bot to automate message responses.