Unclear and Inexplicable Deductions from My Account

This issue of pending transactions is not really clear to me. I am getting dissatisfied and feeling cheated, not understanding how money is being taken out of my account. Why do I have to get penalized for pending transactions, which have already been taken out of my account, just on the note that there were insufficient funds in my account when they were finally debited? Does this mean the bank is deducting money twice from my account? If a transaction is pending, and it has already left my account, don't I have the liberty to continue to spend my own balance until it reaches a zero balance, while the bank completes the payment of the deducted funds on their own end to the recipient entity? Now I have been debited R45 twice for an item paid fee because of one excuse or the other. There is still so many explanations needed around this. I can't just be watching money being deducted indiscriminately from my account.