Bogus SIM swaps security questions

Although Cell C say they do SIM swaps, they dont. I had a SIM card that I use in M2M application that went faulty just after I load it with airtime, databundles and SMS bundles. I never use the phone for voice and I keep "failing" the security test because the "System" ask me what the last number is that I dialled! But I don't dial numbers on that number so it is not possible to give that information! I therefore believe that the "System" is designed not to do SIM swaps and hence Cell-C gets to keep the funds available on the card.