FNB's temporary loan and internet banking app

I am an FNB gold cheque account user, and I took a temporary loan with FNB of R1500, mid December. The loan stipulated that it must be repaid in 31 days (This would be mid January). <br> <br> On the 31st of December, R1800 was deposited into my account, R1000 of this money was not mine and was given to me for safe keeping. I used up all the money in my account during the last weekend of 2015 leaving the R1000. <br> <br> On the 4th of January as I wanted to transfer this money to the owner, my account balance was R0.00! No sms notification was received to show an outflow from my account. I drove to Waterfall mall in North West to find out what had happened to the money and the lady just said that it is written in the loan agreement that FNB can \repay"itself as long as there are funds in the account. I did not know this. <br> <br> To top it all off"