Listed for no reason

Through the years I've been building my credit score and everything was going well until I tried to apply for credit. My application was rejected because somehow my name is blacklisted. How and why, I don't know because all my payments are upto date and my interaction with NDA was about 4 years ago and this nonsense of being listed with debt surfaces now. I don't owe you anything and I don't intend to do any business with you, please remove my name and fix my score