NSFAS sucks

I finished my degree via nsfas and started working in 2014. I sent emails to the scheme to tell how much I owed and what I need to pay. They never got back to me. Last year a debt collection agency phones me to collect the loan. How do you not respond to the initial emails? How when I tell them I can pay xx amount, they call me again and tell me they want to set up a debit order for over R1500 per month on this loan? I have expences as well and also need to eat! How were millions of these loans written off for people who graduated with me, and now I am hounded by you and your detb collectors?