Hi @Kyuu_ and welcome to the Community! 🙂
Since it sounds like you subscribed through another service and not Spotify directly, I would start with Singtel's offers terms and conditions. I checked their website and depending on the plan you chose, it may now see you as a new user entirely. This could happen if you created a new account - which would not be linked to the account you cancelled or previously had with Spotify. There is a support page located here also that Spotify provides regarding carrier/other company subscription FAQs.
Hopefully this was helpful and have a wonderful day! 🙂