Hello dhanh, welcome to our forum. What happens, exactly, when you dial an international number? Do you get a busy signal, or does it not connect at all? Calls within the Netherlands are working?

What brand and type phone do you have?

Please, also, fill in your forum profile with the phone number and sim card number (both can be entered in the ‘klantnummer mobiel’ field). 

You haven't responded yet, dhanh, so I'm assuming the problem is solved. If that is not the case, feel free to respond and answer the questions previously asked.