Hi Sameer,
In your initial code block you were writing to the MUX1 register to turn on the internal reference and route the reference to the REF0 pair. I would change the configuration so that instead of writing 0x38 you write 0x30 which turns the internal reference on and uses it as the selected reference without routing it outside to the REF0 pair. If you have written to the ADS1248 correctly, you should see 2.048V on VREFOUT.
Can you send me some scope shots of your communication to the device? You may see data, but that doesn't necessarily mean that the data is interpreted correctly.
Best regards,
Bob B