Did you know that if you use a search engine you can find answers to things?  Such as:
Survey Sampling International:
SSI is Survey Sampling International, a survey company and has nothing to do with the SSI program by the Social Security Administration, nor does it have anything to do with the Administration itself..  Opt out:  https://www.surveysampling.com/contact/
I don’t personally know if the above link will actually take you off their list, but I have been told a couple of times that it does work.