CLOSED MY CREDIT CARD & NEDBANK IS ALLOWING A DEBI

I closed my Nedbank Credit in 2013 and the balance of my funds was transferred to my absa account. And months later there was debits for plus minus R800 when i queried this with Nedbank they could not tell me who it was that was debiting my account or why they allowed it. In 2014 it was resolved and now in 2016 i received a msg from Nedbank saying i owe them R1800 for that debit. That has now accumulated over the years. My question is how can Nedbank allow a debit to go off on my credit card and after its been closed. Now im getting rude consultants calling me for the money. Lady by the name of faith.And sms saying i will be served by the sheriff if i don't pay back this money. What pathetic service.