MTN Corporate bully

I subscribe to an MTN number for approximately 15 years and have a debit order against the same bank account for all that time. Recently I became aware that MTN appeared to be charging me for blackberry internet service more than a year after I renewed the contract and took a Samsung Mini S4. I emailed the contact centre to ask them to investigate but they refused unless I answereed a variety of their house made rules for their security purposes which I refuse to do. For example I don't even know what my PIN is seeing the account is so old. In response they refuse to attend to my query and continue to take money from my account which I don't believe they are entitled to. <br> My point is that it is irrelevant who queries an account problem. it is MTN's responsibility to audit their accounts/billing and ensure they are billing correctly if they receive information that warrants investigation. There is no need for external customers to be bul**** around by being forced to answer their irrelevant questions before they will attend to an account query. Its inexcusable, especially if they are taking money that they may not be entitled to.