We will not allow the maid using our home adddress, except for the letter from her family.
Actually, the maid can buy the "Add Value SIM Card" and no need to use our home address. I was bought the first one to my maid in the Indoshop and asked her to add value by herself and explained the reasons behind.
In this case, you would better to ask her to open the letter before you. If it is the letter from the phone company, try to see any contract bounded and see can she cancel it.