@dbards , STOP is a very expensive work when you send it to a premium rate number . Just like any word you send to them. And as for fair , of course subjective, however you should know the costs of sending an sms to a premium rate number are huge, and you've gone ahead and sent a text, you should have expected this.
Most premium rate numbers can be looked up on Google and you may find the company in question to request a direct refund as service numbers are purposely purchased to generate this money - just like phoning service numbers on your landline.