It’s really important to think about this thoroughly before you do it because you will loose your community of members who are engaged within your niche. You might lose out in potential clients or customers.
If you want to close down your Paid Club the easiest way to do with would be to message all Club Members to warn them you are going to Close the Club. Then ask them to leave the Club themselves. This will stop all subscriptions including their payments automatically.
Go Clubs > My Clubs > Clubs You Manage > Open Club > Click the three dots > Message All Members.
If you need any help on this please email firstname.lastname@example.org.