How to tell a guy I’m not interested?

I’m a woman who is struggling to tell a man im not interested A few months ago a lady from work gave my number to her son without asking me. Later she told me “you better not hurt or be dating anyone else when you talk to him”

She’s a real life witch and I don’t want anything to do with her or her son. I’ve always been a people pleaser and the creepiest part she only wants me for her son because she found out I was a virgin.

He texted me a few months ago and I was trying to be nice but left him on read so he knew I wasn’t interested. But he showed up to my work and started texting me again. I don’t want to talk to him. I feel pressured and don’t know what to do. The worst part is I have to deal with the lady at work. I’m worried she might tell me “why don’t you reply to my son.”
How to tell a guy I’m not interested?
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