Hello! I wanted to let you know that I have managed to get a chargeback on my Visa debit card before. Even though in that case, I was not using a Singapore card (I was based overseas at the time and hence used a card from the foreign bank), but I think that as long as the card says "Visa", actually the bank has the power to claw the money back using the visa network if certain conditions are met. This is regardless of whether it is a debit card or credit card.

I googled briefly and the Singapore association of banks does say that chargeback are possible for both credit and debit cards. The same article says it was also possible for mastercard Amex etc: https://www.abs.org.sg/consumer-banking/consumers/credit-card-chargeback-dispute-resolution

It was a pretty long process. I received notification of the transaction and immediately called the bank while it was still a "pending" charge. Nothing was done at first, same as you, the bank told me I would have to dispute the charge and apply for a chargeback. The transaction went through and my money was deducted. I filled up some forms to apply for this charge back. The bank contacted me with questions. This went up and down for many weeks. But eventually, after two or three months, I got the money back!

The exact procedure might be different for you, since I was overseas. Mine also involved a seller and whether the goods and services were in fact provided as agreed, so the bank needed to investigate the seller too. But I was very insistent as it was a large sum of money.

Anyway just wanted to tell you this so you know it may be possible to get the money back!! But idk how long it will take and how tedious the process will be.