Best answer by Mathis
That's a 2-step process.
1. Regain access.
2. Delete the account.
Please see here for more info about access: https://help.soundcloud.com/hc/en-us/articles/115003452947-Help-accessing-your-account
If you require further assistance from the team, you can reach out here.
Once you have access again, you can decide whether you want to start using the account again, or get rid of it for good: https://help.soundcloud.com/hc/en-us/articles/115003563188-Deleting-your-account
All the best