FNB Negative balance ****

I'm appalled and basically disgusted by FNB. I recently switched over to this bank from Capitec, meaning my Salary goes to FNB. This past weekend I used my card for the first time and performed transactions that immediately took money from my account. Next thing I wake up on Monday morning and I'm sitting at a negative R3000 but the money I had is gone. I call them and they tell me the transactions were pending. But how when I had money in my account and now it's gone but I'm at a negative? I received 2000 on my account this morning and I wake up to check my account and I'm now at a negative R13000??? I genuinely cannot believe what is going on. I have never in my life experienced this with any other Bank. I regret moving to this bank. If you are thinking of switching banks, please, don't come to FNB!