FNB doesn't protect their clients nor educate them

I'm so disappointed with FNB's system. I made a purchase at shop rite and balance went down drastically and numbers didn't match up. I called the call centre on 16th/04/15 and was advised that their system at times reserves transactions according to the banking system of the particular client. So this is misleading as my cellphone banking will tell me my balance is this much which isn't true. Our banks don't protect us and worse they never let us know of such to educate us so that we are aware of how things work. I'm highly disappointed and i want clarity in writing when this was communicated to me as their client. This will cause bankruptcy to a whole lot of us. I wait for feedback concerning this