How to block outgoing International Calls

I always have this problem with ATT. Though i blocked the international calling long back. They said they cant block the outgoing international calls,  they can just block the incoming international calls. Firstofall I don't lift the incoming international call then what's the use to block the incoming calls. I ended up being charged for a call which was accidental. I want to protect myself against such accidents.So, please let me know how to completely block the outgoing international calls. I am a loyal customer of ATT from past 4 years but this time I am completely disappointed with the ATT customer service as they could not solve my problem.