If I now understand your question better, it is impossible to prevent a user from "sending" a reply to your SMS because the user's SMS app is not your app, so you have no control on what they/it can do. However, you can simply "ignore" any replies if you use the Twilio API.
And to my knowledge there is no "method" to make SMS messages read only. But, if you can find another app that can do that using some undocumented SMS commands, I would be very interested in knowing about it!