You really should find a lawyer.

Generally you have the obligation to inform your Ausländerbehörde about any essential change in your life ("Mitteilungspflicht") and your residence permit becomes invalid when your residence purpose doesn't remain the same (aka when you quit your job). There should be exceptions to the general rule, though I'm not entirely sure here. A migration lawyer should have experience dealing with such situations. They will tell you which steps to take.

Furthermore, having a job doesn't mean that you'll be granted a new residence permit. It depends on whether there is a certain purpose of residence that you can be categorized under. Again you should ask a lawyer if you're not sure about this.