Hey @Jessielong28, when calling overseas, you need to enter some special codes before the number. Check out the full guide here → INTERNATIONAL CALLING & MESSAGING: DIALLING & COUNTRY CODES.
If you are following these steps and it's still not working, we'll need to check your service settings on our end. Jump into Live Chat for immediate assistance, or feel free to send me a private message with your account number, full name and DOB. You can leave it with us and we'll have someone check it out asap.