u just need to add either + or 00 followed by country code, area code and then the number
Let say if you wanna call to Singapore, the dial pattern should be +65 or 0065
Example: +6512345678 or 006512345678
More info about IDD, refer here
You only need to add the country code before the number you are trying to call. For example, calling to Thailand, you need to dial +66 or 0066 followed by the phone number.
If the problem still persist, you may want to contact Live Chat for further troubleshooting as it may be related to your account.