Poor service

I ID no: *** have a home loan with Nedbank I have been banking with FNB . I decided to switch to my salary to Nedbank since I have a home loan with them . To my surprise Nedbank debited from FNB as well for the home loan meaning they debited twice . Why would NEDBANK do that when I switched to them . I have encountered charges from FNB as there were no funds in my FNB account now that I had switched my salary to NEDBANK . I got a call from NEDBANK today claiming that I am R4000 in arrears on my home loan . You debited my Nedbank why did you debit again from my FNB account ??? I want answers please and I want those bank charges I acquired with FNB to be paid by Nedbank . I regret switching banks should of stayed with FNB !!