I'm afraid when things go wrong, Samsung can be truly awful with customer service.
I suspect that the agent thought you had ordered a different or second band.
Please (and forgive me for suggesting this) double check all your packaging just to be 1000% sure the band isn't hidden in the box underneath anything etc.
Then, if no band, I suggest you reply to the email explicitly advising that the green band which is standard with the device wasn't sent and that they need to arrange this.
If still no joy, return it for a full refund then order another one?
S24 Ultra