Deducting Money from my account without permission

I have an overdraft with FNB and they feel that the account is no longer active like it used to be. I received a call from credit analyst by the name of Nthuseng who harrased me because she claims that she has been sending me emails without getting any response from me. She asked me if I want to continue with the account or if they should start taking money to reduce the overdraft limit. I said I need time to think if I will be able to continue using the account or we should agree on amount to pay monthly. She then said she will freeze the account until I get back to her. There was amount of about 7500 in the account which she freezer 7000. I then got back to her, and I said I am willing to use the account or we make arrangement of paying R1000 per month she said she want R20 000 per month she then said R10 000. I explained to her that I can't make an agreement which I know very well that I won't fulfill. The lady then told me that she will take all the money in my account, I said you can't take money without my permission she said she will do it and there is nothing I can do. Some few minutes later she returned R2000.00 of the R7000.00. Until today my R5000 is gone.