thank you for sharing your question with the Wefugees Community!
I would recommend you to make yourself an appointment at your local immigration office (Ausländerbehörde) and apply for the extension of your residence permit. The BAMF is not responsible for that. Here is some information of the immigration office in Berlin as an example for you what to bring etc.:
To answer your question about the re-evaluation:
It is a standard procedure by BAMF that they re-evaluate cases within the next years to see if the protection is still needed. If you received refugee status/protection in 2017, in your case the BAMF has still time to check again your status until the end of 2021. In the re-evaluation they basically check if anything in your country or somehow related to your situation has changed so fundamentally that you are "safe" again and can go back. In German, it is called a "Widerruf". For that you will also most likely get an appointment for an interview, but it shouldn´t be as long as the first one. Still, I would recommend that - if you receive a letter from BAMF regarding a Widerruf anytime - you check in with a free counselling office/centre beforehand to be prepared. But to relieve the stress a little bit for you, they don´t take away the protection in many cases - in 2018 there was only a Widerruf in 1% of the evaluations.
I hope this answer was helpful for you. Please don´t hesitate reaching out to the Wefugees Community if you have further questions!
All the best
Note: Please keep in mind that we can´t provide qualified legal advice via the internet and that any information given can´t replace such legal advice.