If you are trying to delete a specific account and the charge groups as well, sometimes the problem is that there is a Default Charge Group that is set on the customer record, which is why you may be seeing an error similar to below:

To delete this account, Support will need to run some scripts on the database to investigate further. Therefore, please contact Delta Support, referencing the title of this article, including details of the account and charge group that need to be deleted, and a screenshot of the error you are seeing.