NBA League Pass support pages has FAQs regarding package choices, access, account management and billing questions.
You can submit an email question via the online form. They are very good at responding to your questions within 24-48 hours.
To contact a customer service rep by telephone, you can call the phone number 1-844-622-8550 from 11:00 AM EST to 1:00 AM EST. The phone contact is not League Pass specific but hopefully they can help you with League Pass questions.