Don't quote me but I think it's going to stay the way that it is until you finish the rehab and the default is removed. Once the new loan reports you get a boost and again if you get lates wiped.
It's good to start the process if all other efforts end up failing, but to be honest I don't think it's going to matter because I don't see a solution taking the almost-year that rehab is going to take to finish.
I do think that if you don't hear back from the advocate by early afternoon you should call them. If you don't have results, go ahead and file that complaint with the Ombudsman. It will get the official process started and the complaints take a while.
If you can afford legal advice on this whole situation, that would be a good idea to look into as well. I did mine without it but mine wasn't in default. The more complicated their mess, the less likely they'll want to clean it up imo. Hopefully tomorrow will go well for you.
Also, I know the collection fees seen like a small thing in the big picture right now, but don't let them walk away from fixing this in full. This means the collection fees should but be added to your loan. This could easily be hundreds of dollars. If your goal is paying the loan off in full, this will only extend this time. The tax refund should also be applied to the loan, and since it's likely more than the interest payments due, make sure they apply it to your principal. This is a long way down the road but I think it's important that you don't let them cut corners because I've found it you do it'll only lead to having to clean things up later.
When I filed my CFPB complaint and got my solution from my servicer, not only did they give a proper solution, the next few calls I was sent almost directly to a specialist who uncharacteristically bent over backwards to make sure any new problems were fixed. They can fix it if they want to.