Unauthorized email notifications

I've been receiving emails from this retailer for more than a year. I don't have an account yet my email address is being used by someone else for newsletters. I've unsubcribed on numerous occasions and get the confirmation that's it's successfully done yet I'm still receiving these emails. It's extremely irritating and and very frustrating having to deal with a company as big as this and still have this happen. I want this sorted out immediately because I never gave anyone permission to use my information and email address for newsletters.