How to deal with my former friends with benefits who still bothers me?

I had fuck friend over than 2 years ago, we used to close like dating. But he told me he doesn’t want relationship. And we both deal that we just do that like friends with benefits. But i met a nice guy, who wants relationship, and we both dating and officially dating 2 years ago.

I respect my boyfriend, so I ignored my friends with benefits and told him i have boyfriend and I don’t want to do any sexual activity or just see him outside the work. The first time he said that i date my boyfriend because he is rich, and i just want his money. But i never respond him. He also often tries to chat me with spicy texts but I always ignore it. Yesterday he texted me some pics of me (nude) and said that he miss me a lot. And I didn’t respond it. And when he said
“Guess you still with rich guy”.
And I replied him “yeah “. After that he called me but I didn’t answer it.

I can’t block his number because we work in the same place. And sometimes i need to call him.
How to deal with my former friends with benefits who still bothers me?
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