Cell C refuses to blacklist my ****** sim card

Since I was recently assaulted and ****** of my groceries and cell phone, I needed to blacklist my sim card and cellphone. I contacted Cell C's customer care telephonically, after, according to them, failing a security check of which one question was my last dialed number, and most frequent dialed number. I enquired where I failed the security check, which according to their company policy is confidential. Who on this planet knows all the numbers on their contact list by heart? I was in shock, and it was a traumatic experience. My mind is scrambled and now my punishment is that I can't even blacklist my own sim card, after providing them with ALL of my personal details! How can I make them listen and blacklist my sim card?