When I was in the midst of my GW frenzy about a year ago, I sent dozens of GW requests (email, letters, calls) to each creditor. With many creditors, it's about luck.... you need to connect with the right person on the right day when they're feeling nice 
You may have dozens say no before someone finally says yes.
Just keep the GW correspondence going and chances are that you will have luck eventually. I basically had a few 30-day and 60-day lates on all of my TLs (maybe 10 TLs total) from a tough few months. I think I eventually had success with a little over half of them. A few I got right away... a few I got after months of trying and a few never budged and the lates remain, but it was all worth the effort!
