I would not GW again...I would dispute.
I would suggest disputing online with transunion, equifax, and experian. I also suggest disputing over the phone with transunion. You don't have to hold on the line long at all if ever to get a representative, and it's easy to file a dispute. Get a confirmation number so you can check back on dispute status.
Another thing you can try (I did this with HSBC 2 months ago), is ask a representative over the phone if he can forgive your late payments. At first the rep seemed doubtful, but put me on hold, and then said he would eliminate them.
Ethically, I believe this is fine, because you're basically asking someone to forgive you, and if they do then that's great.