Welcome to the forum.
You should contact support. They should replace it for you.
It’s not really charging extra, it’s just breaking it out as an option. Some people already have suitable USB-C chargers, since they are used for many laptops these days. If Framework just included it, and it wasn’t optional, then the price of the laptop would have to be higher. While some of the cables have an issue, the charger is quality and not cheap. Someone made a video of the charger being disassembled and analyzed piece by piece youtube.com/watch?v=XyG8QEe6GIk
I had the same problem happen to me however since. I just picked up another one from the marketplace. I’ll give it the benefit of the doubt once. If it should happen again, I’ll go with another brand. I thought it strange because mine was just wrapped up for a long period of time while my FW was shelved. Then when I went to use it, I saw the plastic had split. I was thinking maybe the plastic was stretched(stressed) too much and that is what caused it. Personally I love braided cables (my MacBook Pro cable is the best).