Most likely, you will not be able to delete the account on your own. Contacting the Support is not helpful, because they will offer the self-exclusion service, which is not the same. The most reliable way is to leave the account dormant, to mark all email notifications from the casino as spam, and wait for around half a year until the casino deletes the account on their own. The only thing to do before that is to delete all information from your account, including banking details.