You really need a lawyer to deal with this. The best solution to know about your options and find a lawyer is to approach a refugee support group like the ones mentioned by Zach.
As far as your immediate situation go, you have to read the letter very carefully. Typically, what happens is that you applied for protection and the authorities have determined they might have grounds to ask another country to take charge of your application. Germany has to inform you that it's trying to use the Dublin regulation but, at this stage, you are under no obligation to leave. You can ask your lawyer to make representations on your behalf and Germany needs to wait for the French authorities to respond to its request anyway.
It's only after France accepts to take charge of your application and a decision is made that Germany will officially decline to process your application any further and may even detain you to bring you to France. You do have the right to make an appeal but, again, you really need a lawyer and even with a good one the chances of success are slim.
Unfortunately for you, France and Germany are two of the few countries where the Dublin systems still works and the facts of your case, as described in the question, do not look very promising. You really need to get in touch with someone who knows the law and local practice to navigate this situation.