Edgars is trying to rob me

Over 6 years ago I settled all my accounts, this included the Edgars account. However about a month ago I started receiving calls from a debt collecting agency called Nimble saying that I owe Edgars over R300. Now you can understand my confusion because I no longer have an Edgars account and whatever was owed to them was settled years ago. Initially I ignored the requests but as the calls frequented I decided to call these people to find out what was going on. Surprisingly, mo one (between Nimble and Edgars) could explain what happened before the account was handed over and why there was an amount that was outstanding at the time I closed the account. I spent over 2 hours going back n forth between these two companies and I have officially had enough. I want someone senior from Edgars to call me and explain what the problem is and how they're fixing it because I am not going to pay for something I dont owe. This is very urgent