XFINITY OWES ME$ 670.40

I have been waiting since april for xfinity to refund me. I transferred services in september but they continued charging me for my old account that they should have closed out. I called in april when I noticed and they have been giving me the runaround since then. I keep being told that they will refund the money, that they will call me back with a resolution,but they proceed in sending me a text saying case was closed and dont call me back. I AM OVER IT