I used to study in Germany and graduated recently. According to § 16 AufenthG I have the right to work/reside for 18 months afterwards in Germany.
When I was leaving the country I deregistered (Abmeldung) from the city that I was residing in. Just three months after my deregistration I returned to Germany.
At the Bürgeramt I have been told that since I have deregistered I cannot ask for prolonged stay in Germany anymore.
Since the woman I was talking to seems to discriminate her clients I was wondering whether there is a law that states that after deregistration one cannot extend his/her residence permit.