1 derogatory mark & we can’t get a HELOC

We were scammed in 2012, paid off all debt, but 1 collections account which we pay monthly. Our credit score is 673, DTI less than 2%, we own our home, & have excellent “pay on time” score, but were denied for a desperately needed roof loan. We’ve only had 2 credit checks in years, but I don’t want to run that number up either. I really need some direction