One option would be to sue the BAMF because of inactivity.
There is at least one case in the media of someone from Sudan who sucesfully did this, because he waited 16 months already - which was not acceptable in the eyes of the court.
More and more people are chosing this way, because of the long time which has passed already.
In the meanwhile in Düsseldorf's admininistrative court it seems to be sufficient to state at the Rechtsantragsstelle, that you are planning to sue the BAMF.
Your name would be set on the list and passed to the BAMF. In such cases it is said that the process has been sped-up, because the BAMF tries to avoid the costs of a legal process. But it does not mean that you get a positive reply in the end.
This is all just info I caught up from the media. Neither do I know the rate of success in your case, nor which would be the responsable administrative court for you.
If you think about going this way, I would recommend to consult a lawyer near your place.
Here are the articles I found on the web (only German):