Dropped Calls

I have been an Xfinity customer for about 3 years. In the past month or so, my phone drops calls regularly. I will dial out and it disconnects immediately. Then the person tries to call me, it rings, and when I go to pick it up the call drops. This will happen every time that I try to call out or somebody calls me. The only way that I can reset it is by turning my phone off and turning it back on. Then a couple days later it will do the same thing.