I responded within a week of receiving the letter. I didn't notice the fake date on the letter initially, and threw out the envelope after opening- so it's lost

I responded within a week of receiving the letter. I didn't notice the fake date on the letter initially, and threw out the envelope after opening- so it's lost forever. Yes, I of course used certified mail to respond to them. I had not spoken with them before the letter. I will of course try the credit bureaus, but in my experience everything takes 30-60 days to get an initial response etc. At the speed they move at, likely sinks my ability to buy a home this year. Hence my interest in a more aggressive tack