survivors benefits for my 2 children

I desperately NEED help. My children are 17 & 13. Their father passed away June 17, 2002 on fathers day. At the time they were 2 & 6. I applied for survivors benefits for them immediately after. But I was told that they didn't quality for a dime because he didn't have enough work credits. Afterwards I was also denied 3 more times. Me & their father lived together since we were 19 until his death. He was 27. We obtained a marriage certificate when I was 7 mos. Pregnant with our first child. I also have paternity results proving they were his because of a turbulent split. How do I go about receiving survivors benefits for them. It has been a nightmare trying to support my kids with no help. I have no one. It's just me, Morgan & Donnie. Please guide me in the right directions. My children deserve much better. Thank you so much, Brandi