Hi
You indicate that the service provider, I assume you mean Vodafone, must inform you about the costs. That is not true, the owner of the service number must inform you about the costs. Your contract with Vodafone, with unlimited calling, does not cover costs that fall outside this unlimited calling. Of course, Vodafone cannot block your call because you incur high costs. You always have your own responsibility. There are indeed additional costs for calling a customer service number, outside the EU and within the EU. See the rate example below and also see the URLs already given above.
By the way, I do not work for Vodafone, just like you, I am a Vodafone customer. And because I have experienced this problem myself, I can speak from experience. It's annoying and something to pay close attention to next time. *I translate in Google*