Bluetooth issues!
 

Unfortunately this is a confusing and possibly expensive fix. I did a ton of research last fall to get this to work for my 2006 c230, which was not "prewired". Here is what I learned, prewired, does not necessarily mean that it has all of the components to make the Bluetooth work, though it might. I bought all of the OEM components on E-bay. It took a while but I was able to find most of them new in the box. First, I installed the Bluetooth dongle in the armrest (which you already have), and installed the Bluetooth puck (which you also already have). From what I've read, this is mostly what "pre-wired" is, which is not enough to get the phone to actually work. At this point I was able to pair my phone, but like your setup, nothing actually worked though the puck flashed a blue light and the phone said it was paired. Very frustrating.
I then had to add a Bluetooth voice command module, per the e-bay listing, it's part number A2308207026. For some reason, which more intelligent people on this forum can probably explain, there seems to be a lot of Mercedes parts that look identical but have different part numbers, and some are interchangeable, some are not. This adds to the confusion, but might make more parts available if you're going the e-bay route like I did. Anyway, it's a silver box with a spot for power input and audio input and output. I believe everyone has the power plug in the trunk and that was the easy part. The extra audio / fiber cable you'll need should also be there (wrapped in a foam protective cap). The hardest part was determining the correct sequence to connect the audio. I'm assuming the C320 uses the same fiber optic for the audio as the c230, but again maybe someone will let us know if that's not correct. Although I found the directions on-line, and read how others have done it, everyone whose posts I read had a slightly different setup than mine car. I have the command / GPS OEM head unit, OEM 6 disk changer in the glove box, and OEM satellite radio. Every component has a fiber in, and a fiber out. One fiber in comes from the command unit to the trunk, into the first component, then out from that component, and into the next, and so on. They have to be set up in a specific sequence to form a "loop". The correct sequence is different for everyone depending on which components they have. I literally spent hours trying each and every possible scenario until it finally worked. Basically, I left the key in the on position and started with the first fiber optic cable that had a red light coming out of it, and plugged that into the input for the first components, and kept going until finally I pressed the phone button on the radio, and it worked.

I have an IPhone 7 which works perfectly with the system. I can call from the command unit and everything displays properly and sounds great. All other components work perfectly as well. I believe basically any phone will work once you have it set up.

https://mbworld.org/forums/c32-amg-c...omplete-6.html

Don't forget about the ///AMG Forum...you may be able to find more options to help there.

Yes!! I used that post extensively. Unfortunately I could not find some of the parts they used by the numbers listed, and some of the links no longer work. That's just the way it is when you're working on a 12 year old car though. Also, some were getting the parts from their dealer, I'm not sure if that's an option still. I attached a document I found which is for sat radio install, but shows the loop setup. Again, mine only worked by trial and error, but it might help in your setup.