Bicycle detail

I got a bike from my aunt as a gift, it's new and I don't have any photos of the bike (I attached the photo from the website. My bike exactly looks like it. The speedometer is even still wrapped with plastic!). It's radcity step thru-3 (white color). I locked my bike in the railing on my porch with a U lock & cable. When I want to use it in the morning (November 26, 2021, around 8-309.30am) I found that my bike was stolen, and somebody cut the cable. The U lock is still attached to the railing (as you can see in the photo). I'm 100% sure I attach the U lock to the bike frame. I've no idea how the perpetrator did it.