I first tried to contact the Sunrise Hotline (in French) but with few results. Having had no news from my first call after several days, I contacted them 2 other times and I had to explain them each time from the beginning.
The French hotline seems to be outsourced abroad and I am not satisfied with the service at all.
For my last call, I called the English hotline which was much more efficient and was able to give me the clear answers I was expecting.
I also found this Sunrise Community to be very helpful and very responsive in answering me. Very quickly after sending a private message, they switched me from IP v6 to IP v4, which solved the first problem by allowing me to perform port forwarding again.
However, the DynDNS service is still not available on the Connect Box 2. So I asked to replace it with the Connect Box 3 which would offer the DynDNS service but which is currently out of stock.
I am in the queue to receive the new router as soon as it is available…
Here is what I found out from my experience
1/ Avoid if possible the French hotline
2/ Preferably use the English hotline (I have no experience with the German hotline because I don’t speak the language)
3/ The Sunrise Community is also very efficient and fast but will not be able to solve everything for you without going through the hotline for some requests.