FNB - Debit Card Dispute

I rented a s****** while on holiday, after returning the s****** I received a void slip for the deposit paid. 30 days later the money gets withdrawn out of my account. After numerous attempts to resolve the matter with FNB and the merchant I receive an email from FNB stating "Kindly note the merchant did not bank the transaction". So where is the R4 022.00 deposit if the merchant didn't bank it but the money is subtracted from my account?? Worst service I ever received from FNB and I've been banking with them for more than 10 years and also have 2 business accounts with them where I've never even talked to a relationship manager because they are non existing! #REF:***