I haven’t found other documentation on this issue, but just about every tech support scam center I call (even if they are 1800 numbers) responds Unavailable or Busy. I not making any more than ten calls in a day, so it can’t be the limit set in place. For example, this number works very well: 18552579669. This one, however, responds Unavailable: 18443242962. I figure that it can’t be a country calling issue, as they are both 1800’s. Any help would be appreciated.