You may not want to report it to the police but harassment at this level can be stopped by speaking with someone from a group that works with the police. Not sure about your area but in the north east its called Arch, and they class it as a hate crime. I had to call them recently and they were very helpful and now have the texters number on file so if it happens again they will approach the police on my behalf.
I can understand being afraid of these unknowns texting, my boyfriend also got texts from the same person texting me, which was worrying as he isn't involved in my work at all! But you can't live like that.
If you want to avoid the problem you can get an app for your work phone (if you're using that kind) called blacklist which is really good too
Good luck and take care
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