If you purchased iRacing from www.iracing.com, your account is set to auto renew by default.

You can turn this off by logging into iRacing and go to Account...My Account - scroll down the Billing Options section and you can turn it off here.

If you purchased using PaymentWall, you will need to contact PaymentWall Support or turn off the auto renew in the PaymentWall website.

If you purchased iRacing through Steam, you will need to contact Steam Support.