International calling Plus doesnt work

I recently purchased a prepaid Vodacom sim card because Vodacom has advised cheapest international call rates in SA. after buying the sim card and purchasing airtime and the R5 per month international calling plus service. Every time i try and make a call it just says network busy..... YES i am using the correct number and YES i have tried calling the number from a landline and it goes through - I have even inserted my sim into another handset, after dealing with several Agents no one is able to assist. Is this false advertising on vodacom's side or is there a problem i need to know about? Can someone please assist as i really need to be in contact with someone in Nigeria.