FNB inconsiderate of its client

On 25th February(payday), two unauthorised and unknown deductions of R4008.21 and R4008.22 were made from my current account. I've been struggling ever since to get resolution on this matter with no luck. How difficult can it be for a bank of FNB's stature to determine legitimacy of such transactions and refund client back? Why should I continue to be inconvenienced because of the bank's failure to protect me as its client? They're not doing me a favour, I pay for the service? I'm quite certain that I can't be the only customer inconvenienced this way, and I feel it's unfair and *********. I can't afford to have R8000.00 deducted from my account just like that, I'm not the bank?