Dear Ali foroz,
Welcome to the Wefugees Community and thank you for reaching out to us!
Applying for a permanent residence permit (Niederlassungserlaubnis) requires to hand in many documents and information to the immigration office (Ausländerbehörde or in Berlin "LEA"). Please check the confirmation letter carefully again - are they asking for any additional papers or information from you? Don't forget that they may also contact you via email. In any case, I would recommend you to get in contact with the person responsible for your file at the immigraiton office directly. You usually find the contact details (email and number) on their letter in the upper right corner. As it is indeed difficult to reach the immigration office staff via phone, it is the best to formualte your issue in an email. I am sure they will get back to you!
It is always difficult to predict the amount of time they will need to work on the application. Additionally, the immigraiton office needs to prioritize in the Corona days, which means that waiting periods will most probably longer than normally.
I hope this helps and all the best,