Complaint over unknown debt

I have been receiving annoying emails from MBD Inc which claims that I owe them R19417.88 for the debt they bought from Absa bank. For the record, I don’t have any account or debt with Absa. I therefore cannot be expected to pay for something I know nothing about. They must stop harassing me with their stupid emails. I need the original proof of the debt from Absa, stating what was the debt for, when was the account opened and when was the last payment made. They must also furnish me with the debt agreement (showing my signature, ID documents, payslip) and telephone conversations of my consent. Otherwise they must forget about because I will not pay for something I know nothing about. MBD is notorious for taking chances and harassing people about nonexistent debts. This is a law firm of ****mers.