********** cheques debited against my account.

My problem started on 10 December 2014 when i received a notification on my phone notifying me that a cheque of R475 000 was debited against my FNB account, which i don't know anything about. I went to Bank City branch to get clarity on this matter and after waiting for almost 2 hours in the branch they managed to get a copy of the ********** cheque. The cheque appeared to be genuine cheque but the signature is different to my own. The last time i had or used FNB cheque book was in 2003 and suprised and shocked that someone managed to obtain my cheque book and is using it **********ly. I went to several FNB branches to report this but was told that they can't open a ********** case as no money was lost. In January 2015 there was another cheque of R32 000 drawn and today 04/02/2015 there's another one of R182 000 drawn again. I'm dissappointed with FNB for failling to protect their customers against such ****s especially after being a loyal customer for more than 10 years. I would like this matter be resolved urgently and all my accounts be closed.