Hi!
Yes, I spoke with my lawyer and I am quoting her email: "You are absolutely right, the embassy made a mistake when it changed your category from Immediate Relative (IR-2) to a family preference-based category (F-11). Your age was frozen when your step-mother filed an immigrant petition on your behalf, as such you are still an immediate relative and an immigrant visa should be available to you now."
We are now trying to get hold of the embassy. I already tried contacting them but had no reply. I got my lawyer to contact the embassy so hopefully we will hear back something soon about changing the visa class back to IR-2.
Hope this helps