FNB and their crazy bank charges

I’m getting frustrated at my favourite bank. My balance reached -996 for reasons I do not know as I don’t have an overdraft facility. I was told by one of the consultants that I have grace to swipe up to R4000 with no funds in my account so now I exceeding my balance and then started using their money. I explained that for every instance that I swiped my card, I had money in my account so why is it that now all of sudden I have exceeded my balance? And they even charged me R180 for a declined transaction and I asked about it and they returned that money to me.

I was told my money was going to be reversed, as R10000 was deposited into my account from my investment and R9000 was left after that. I have been following up with FNB about that money but still no proper feedback. I need the money for petrol and now I’m stuck. Can someone please assist in me getting my money back? I have left FNB before when they too R800 from my account that I could not understand why and they are doing it again. This is starting to get ridiculous. I love my bank but yoh, they charge an arm and a leg for stupid things.