Roommate owes me and other tenant money, won't pay

I live in a state where the security deposit remains with the lease until the unit is vacated all at once. If one person moves out and others stay, the one leaving is sorry out of luck when the deposit is concerned. So when I moved in, the deposit had already been paid, but not by anyone living there, as that person(s) had already moved out and signed some type of form that released the deposit to the future tenants.

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Well, when I moved in, Bethany, one of the tenants, told me to zelle her $1000 for the deposit. She said she had paid it, and I needed to reimburse her. I can see a deposit on file, so I thought she was being honest and I gave her the money.

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Another tenant moved out a year later, and Lisa moved in. Lisa was asked by Bethany to give her $900, so Bethany could serve as intermediary, and reimburse the departing tenant. Well, after speaking to the office, it turns out that Bethany had kept the money in her own bank account. No one paid deposits except the first people who left years ago.

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Lisa has been trying to get Bethany to pay her back, but she won't. Lisa suggested not paying Bethany for internet, as it's in her name, but Bethany said she'll just change the wifi password if she doesn't pay. Also said she can't take the internet fee out of the $900 that Bethany has. Also every time someone comes in the apartment and Bethany is in a common area, she runs in her bedroom immediately. I'm also not being as aggressive about it as Lisa, so Bethany is ranting to me constantly by text about Lisa and it's driving me crazy. I'm afraid of doing something I'd regret. Don't want a tenant to leave and then I'm stuck paying their rent. Please help.