You've been MagicJacked!
I have seen many homes and businesses switch to VOIP over the years, hopping on that hypegasm rainbow-____ing unicorn of hopes and dreams, and not once have I ever seen it come even close to being equal. Call quality goes down. Networks get overloaded. Downtime happens. Costs are shifted. And at the end of the day, after fixing everything that you can, the best you can say is, "It's almost as good and we certainly cannot go back now." Why anyone would voluntarily choose this nightmare today, after all of these object lessons, is only willful blind ignorance.
Oh, sure, in theory it could work ... if you first invest properly! But no one ever does. No one. Ever. Does.