***** and FNB doesn't care for their client

So I have been banking with FNB for a while now I even have a business account with them. June I realised something off with my funds, I went through my statement only to realise I have two unauthorized transactions from FFW and Auto and general, no debt mandate from either one of them. I called FFW with the reference I got from the tempted debt, the lady mentioned that the name I have given doesn't match with their client who is using my account number for their insurance, I have called FNB and made them aware of that's happening with my account I didn't get help, I locked my personal account and even made FNB aware that it will remain blocked until this issue is resolved. No one from FNB HAS CALLED ME REGARDING MY COMPLAINT, INSTEAD I GET A LETTER FROM THEM SAYING MY ACCOUNT IS OVERDRAWN CAUSE OF BANK CHARGES - R3200+ to be exact, I have expressed my concerns... FNB has ridiculous service to their clients! How am I supposed to pay that amount when I have blocked it cause of these ***** ****s