South Dakota doesn't have a specific auto-renewal law, but the DTPA (no specific auto-renewal law) (S.D. Codified Laws § 37-24-1) plus federal FTC rules protect your right to cancel.
S.D. Codified Laws § 37-24-1
Penalties: Actual damages plus civil penalties
SubScrub automatically cites S.D. Codified Laws § 37-24-1 and federal laws