Welcome to the Wefugees Community and thank you for reaching out to us.
First of all, I am really sorry to hear that you are struggling and find yourself in such a stressful situation. I am not a lawyer but have my doubts that it is legitimate that your lawyer did not inform you about the court's letter and invitation - only because he/she is expecting you to pay a bill first. Since I am not very familar with your case and your background either, it is difficult to advise you on the next steps to take. I think in your situation it will be the best to get individual (emotional as well as legal) support in a refugee/migration counselling office. In such an office the social workers can help with the communication between you and your lawyer and keep an eye on his/her actions. I assume that you applied for a residence permit as father of a child holding a residence permit in Germany ("Aufenthaltserlaubnis zur Personensorge")? This type of residence permit was discussed a few times already on this platform. As a colleague explained here, is is not very easy to get and applicants are not entitled (the issuing will be at the discretion of the immigration office) to it. However, this does not mean that there are no perspectives for you to stay in Germany. I don't know if you learned about the current government's plans already, to introduce the so-called "Chancen-Aufenthaltsrecht" for people who hold a Duldung in Germany since many years? As I mentioned before, I would highly recommend to get some individual support (i.e. in a counselling office which you may find via this search engine) or via the MBEon-App (more information in the blue box on the right).
In any case, please also don't hesitate to get back to us with any further questions.
All the best,