Penalised for using available funds on my savings account

I would like to know if I am the only person experiencing this, every month I have charges on my savings account for dishonoured fees for purchases made. I keep querying this with FNB but always seem to get the same story, to check my transaction history etc, so I keep ignoring it and continue month in and month out because querying it seems like such a painstaking process and the agents don't seem to really know how to efficiently help.

This month my account is overdrawn with over R2000, I'm told that it's because I used my funds before the deposits were cleared. How is it possible if I don't have an overdraft facility. I understand that the merchant only banks the purchases a while after but still, when one makes a purchase it is immediately taken from your available balance and one even receives an in contact message proving this. So how on earth can one's debits exceed your credits, this just does not make sense to sense to me and seems like a very easy way to make money and an even easier way for me to lose money. Why then make the deposit form part of the available balance if they're saying its not actually available and why do purchases get deducted from the available balance if its actually only banked days later? to me, that's a clear credit and debit, so whey be penalised...

I might as well have a cheque account because this is what I'd expect from a cheque account, not a savings account. To my knowledge if you have a savings account you can only use the funds you have available to you, no hidden stuff, there's only a current balance and an available balance. What's changed now? I've had this account for many, many years and it is just lately getting out of hand. If a deposit is made into your account, it's made available on the system to use, but the bank penalises you for using it, also, your purchases are immediately deducted from your available balance. So how is it dishonoured?it this not a duplicate of fees?

Someone needs to review this because the call agents are not much help.