If you have returned to your country and your Singapore card has not been canceled, it may cause the following problems:

1. Damage to your credit record: If your Singapore card has outstanding debts , your credit history may be affected. This may affect your ability to apply for credit cards, loans, etc. in the future.

2. Additional fees: If you do not cancel the Singapore Card, additional fees may be incurred, such as monthly management fees or annual fees. This may place an unnecessary financial burden on you.

3. Legal issues: If you have a bank account or credit card in Singapore and do not cancel it, you may be subject to Singapore law. If you fail to comply with relevant legal requirements, you may face legal liability.

Therefore, it is recommended that you contact the relevant bank or credit card issuer in Singapore as soon as possible to cancel the Singapore card that you no longer need to use. If you are not sure how to handle it, it is recommended that you seek advice from the relevant agency or lawyer.