Poor managing of our accounts

I have bank account with nedbank, I found out that they had been having trouble where they debited customers in error twice, I had been refunded one, but yesterday was shocked to see debits to the amount of 9000 to may account for purchases I made in the month of May which was debited even in May, I spoke to nedbank who confirmed I was debited in May and now again in September the same amounts from 2 different stores on the very same date, I find that odd that it's not the bank and 2 different stores debit me the value of 9000 on the same date. Nedbank days I should take my bank statements now and run to the stores to refund me those amounts, my question was how does a bank we entrust with our money allow this amounts to go out of the account. Also I did not have sufficient funds and they drew the money still. I feel the bank is responsible for this and not the stores cos it was a debit to 2 different stores in a single day. Now I'm told I must face the costs, my calls cost bank statements cost, fuel to go to the bank and the stores they claim are responsible for this.