Paying to see who calls on a contract cellphone

I have a contract at Vodacom where i pay a reasonable price every month, and i just phoned a consultant asking why i have to pay an extra amount to see who is calling which isn't right at all, to know who phones me during the day for business purposes i have to pay an extra fee, WHY MUST I PAY TO SEE WHO PHONES ME? I was also told to pay this fee every month.