Wrong Number 1, 2 & 3 .....

How long should it take for someone to figure out that they are calling the wrong number? About a month ago, I started getting a call from a specific prefix out of town, but still in the same area code. Of course at first I would answer, never knowing if it was for me or not. They would always say, "Sorry, wrong number" and then sometimes call back again, 2 or 3 times. Then, after a while, I would recognize the number, but not be sure who it was, so I would answer. Again, "Sorry, wrong number," but still she would call 2 or 3 times. Cell minutes being at a premium, I saved the number as "Wrong Number" so at least I would know that I didn't need to answer. They keep calling, and they must have a work number or something, because I now have Wrong Number 2 and Wrong Number 3 saved as well. I have probably received 50 or 60 calls from Wrong Number. Wrong Number 2 called this morning at 8 AM, and I didn't answer. So she called right back. This time I answered and said, "Hello" she said, "Sorry, Wrong Number (how did she know I called her that?)" and I said, "Wait a minute, You call here all the time. Would you please write down the right number, because I work nights and you just woke me up!" Wrong Number hung up on me. Not even a "Sorry" or anything. But at least she didn't call right back.