SEO - Can SEO work be done without access to my store?

Hi everyone, new to SEO here but have a long standing website from 2017. Never used SEO services in the past because they were just too expensive and we were strapped for cash at that time. I recently am running the business again and was pitched SEO services pretty aggressively lol. I decided to sign on for $500 for the first month. Because it was a busy holiday season, and partly because I don't trust giving access to my site (they even asked for Admin access!), I never got around to it. However, I got a recurring $500 bill the next month. The agency (pretty sure India based) said that they had already done work on the keywords and everything, even without any access to my site or any information at all. I guess my question is - is that possible? Is it possible to do SEO work without having any access whatsoever for the website you are doing work for? Real SEO noobie here so I feel like I can get taken advantage of quickly in this space. Any insight is appreciated. Thanks!