Damelin correspondence college

I registered last year but my student portal ddn't work and I did not receive any study materials from them, I tried contacting them countless time by phoning them and even sent emails but I never got any help. So I decided to stop paying because I was not studying now the call me almost everyday to tell me tha I owe them they even put my name on credit bureau... I told them I want to deregister and they should refund me because I never benefited anything from them but I paid the registration and 2 months installment.