Doubtful operator

I received an email from Nu Debt Management demanding immediate payment of an old Telkom debt. I admit that I owe Telkom some money but not the amount they had been claiming. I have been requesting a statement of account from Telkom and subsequently their debt collectors, on a regular basis for more than 2 years without any response. Nu Debt made me an offer for a reduced amount which I deemed reasonable. I proceeded to make payment using the easy payment link in their email. After selecting my bank and providing my account number, they requested my login details. To me that is a no go. Please be super careful when dealing with this company.