Don't blame yourself for fucked up banking practices.
Once I went over my credit limit on a credit card by like $5 and they charged me a $35 overdraft fee. I called them and angrily explained that the whole point of a credit card is that there's a limit to it, am I expected to keep track of all my credit card expenses and make sure I don't go over the imaginary, practically non-existant limit?
They couldn't help me and I told them to sod off and tore up my card. Now they call me every month begging me to get another card with them, but I've moved on to another bank and don't even pick up their calls. Now I bet they're sorry.
I know my situation is different since it was with credit, but I've had all sorts of other problems. Banks are evil, all you can do is learn from your mistakes and remember those sleazy practices so they don't get you again.
Edit: You know what, it sounds like your situation is even worse. The whole point of a debit card is so you're using actual money that's sitting in your bank account, letting you spend money you don't have is what credit cards are for. Plus, as far as I know over here you need to apply for an overdraft limit on your chequing account and obviously need to have a good credit record to get it. Did you ever even apply for such a thing?