Lightlegacy

My Score now is 643 from 642. I nearly paid off everything except my car note and student loans (Which are on time or paid early). I use my credit card frequently and pay them off over the course of months but my score hardly moved. I did have a charge off from a Sears credit card years ago (almost 7 to be exacted) that I paid down as a settlement, but in the last month, a collection company decides to call me and collect on it. My question is: 1) Even when I settled on a debt, can a collection company still come after me? 2) Is this what is keeping my score from going up? 3) I am 7 points shy from 650, any tips on getting me there?