You can check your prepaid balance via:
SMS
SMS 000<space>12-Digit-Smartcard to 66688
Example: 000 012345678910
* Standard telco charges and Terms and Conditions apply for all SMS
NJOI Prepaid WhatsApp
Step 1: Send Hi to the NJOI WhatsApp number (03 9543 8100)
Step 2: Key-in 1 for Credit balance & Top Up