Handed over with no contact

I opened a cheque account with Absa last year in 2018 and due to unemployment i had no funds going into the account. Now I am getting a call from Nimble attorneys or something like that telling me I ow absa and my account has been handed over. At no point did absa contact me themselves and make me aware of any charges but now I am being threatened by collectors. I have not changed any of my contacts and absa could have contacted me first. No consideration for their clients. So quick to handover accounts