How to make sure my plan is auto renewed as needed so I never run out of credits?

Your plan will automatically renew once you have exhausted all your parsing credits as per your plan or the plan validity has ended.

You can access all the information regarding your plan from the My Account panel., here are the steps for the same Where can I see my plan details? – RChilli HelpDesk

If you still have a question, you can always contact RChilli Support via creating a ticket at RChilli HelpDesk or by sending an email at support@rchilli.com.