This is still happening in 2017. After 5 days of 15GB data, I turned off the data. Then the next day I just use the prepaid mobile app to purchase a new package. While browsing the app, the balance decreased in my very own eyes from $17+, $15+, $10+ until only $7+ left. Called 1633 and gotten back the balance. Reason given was that after promotion period, the system will deduct my past usage during promo period from my balance if I do not have any data plan. What on earth such kind of system exist in 2017? How many users will be affected by this issue?
Few days later I purchased 3 days 1GB plan and ensured I did not use up the data or use data after expiry date. I can check the data usage real time from prepaid app. Today, my balance reduced to 5 cents without any call, data usage all all! Have to call again and CSO mentioned as a good will he will refund x amount to my balance. I am not sure I should thank him or your incompetent system. This is not right and there are plenty of such complaints in this community. Time to look into your usage tracking system. It's full of bugs and rob your customers of their balance. I hope I am the only unlucky one that encountered such issue.
Yikes! Sorry to hear about the experience you had @Bright Tim. Please PM me the subscriber's name, NRIC/FIN, E-mail address and contact number. We'll be in touch. - Sofia