1. Yes, you should still receive payment.
2. You also have a right to obtain a favorable appraisal. There is a special language code in Germany for these appraisals. You should hire a lawyer doing labor law in order to obtain it.
If a lawsuit is necessary, be aware that before labor court every party pays its own lawyer not matter which is the outcome of the lawsuit. This way, lawsuits are not too expensive, but check the costs beforehand when contracting a lawyer.
3. These bodies are called "Rechtsanwaltskammer" and do exist for every state (Bundesland). You can easily find them via Google.
You can also claim just the receipts, if necessary in a lawsuit before the labor court (Arbeitsgericht). This should not cost a lot of money even if it is necessary to go to court.
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