ABSA bought credit card by MBD Legal

I am being harrassed by ABSA lawyers MBD Legal,they are calling me almost every day saying they have bought my Credit Card debt of R2700 from ABSA & I need to pay them.ABSA have cancelled my debt on Experian now it's MBD reflecting on my credit report saying I must pay them.I don't know this MBD people,I didn't enter into a contract with MBD but they are reflecting on my credit report.How did this people end up in my credit report because I have not signed anything with them.I called MBD and ask them why are you on my credit report?The said they bought my Credit Card debt from ABSA.what is this?