Trademark Infringement

California

I need some help and direction. I own a registered name with a logo for my business. It is a small business but I am moving it along everyday. I have products made with my mark. My business is a women's clothing apparel line that is for fitness wear and boxing wear and equipment. Today I was searching the internet and found a website with my name with a slight variation, but they are using my exact name to run women's boxing club shows and they're are selling tshirts with the name on their website. My question is can they legally do this? Is this an infringement of my mark? And what can I do about it?

Please help!

Which company was in operation first? Where are they located?

Also, I'm a little confused: first you state that it is similar to your name but with a slight variation, but in the same sentence insist that it is the exact name; which is it?