@mavenboard -- can you configure your small program to use some other port, e.g., 8888, to see if that port can be reached from the Internet, and also from a device inside your local network? Remember to enable "port-forwarding" on the cable-modem to the computer running that small program.
Note: using "data" means that your device is connecting via cellular to the public Internet, and then through "port-forwarding" to your "host" computer. That's not different from any other notebook/desktop computer on the public Internet, i.e., nothing "special" about using "data" to connect to the public Internet.