Find your sister, your maid, you, all 3 go to the bank talk to the people who borrow money to your maid. Find out why she can use your sister's telephone number. Settle this thing first.
Don't worry, you're not the one to borrow, they can do nothing but to disturb you or your sister, but sure was very troublesome.
Just take the maid down to the bank, ask them why they borrow money to her, and now she can't payback, just ask the bank to chopped her into many pieces that's all. Ask the bank not to disturb you and your sister.