Not honoring their mistake

I was told that my debit order was not going through I must pay cash, they will stop the debit order. I did made the cash payment only to find out they re issued debit order and I had to pay them twice the amount, when I query this I was to that it was late for them to stop it and they made it my problem they couldn't even reverse the money immediately I was to to wait of which I had debit order needed to go through of which I was charged unpaid since there was not enough money on the account of which that hurt me a lot. I was so disappointed. This month of December I requested reversal of the amount that was not authorised and the lady assisting me reversed wrong amount and when I called back they guy told me he cannot assist me I was call the transaction centre to re process, what a shame, how come I must bear all the troubles for the error that was done by them, This is not acceptable in any case, disappointing I am so upset. its a pity we have to beg and take a fall for these banks.