SoundCloud can now text you login and account-recovery codes, and it says your mobile carrier's message and data charges may apply. The charges come from your phone company, not SoundCloud, and the texts are for account security rather than marketing — but it's a new cost you could see if you pay per text or are roaming.
“Message frequency varies; Message and data rates may apply; Text HELP to +19175469191 for help; Reply STOP to cancel”
What you can do — If you don't want these texts, reply STOP to cancel them — but note that turning them off may block two-factor login or password resets, so set up another recovery method (like an authenticator app or a backup email) first.