If you dream of calling for help but the phone does not work, it means you were anxious in your previous day’s waking hours. Your worries created stress. And that mental mood was carried forwards into your dreamworld. Your dream reflected your state of mind’s present theme.
Another dream interpretation is that perhaps you felt frustrated that you had reached out for help, but didn’t receive the necessary aid. Your appeal did not work for you. That triggered the dream of using a telephone which did not work.