Why is Snapchat banned on my iPhone?

And that is something you'll have to address with Snapchat. Apple has nothing to do with them. If they banned you, only they can unban you. The fact you've tried to create a new account, means they have not only banned you, but your device.

But no one here nor at Apple can do anything to help you. You have to reach out to Snapchat yourself.

https://help.snapchat.com/hc/en-us

SnapChat banned your phone. Only SnapChat can remove the ban.

Contact SnapChat and ask them to remove the ban on your phone. This has nothing to do with Apple.

https://help.snapchat.com/hc/en-us

Only Snapchat can unban you or your device.

Neither your fellow Apple customers posting on this forum, or Apple, banned you or your device from Snapchat. Neither we nor they can remove the ban.