Called 1-866-797-1313 and it said there is a new national number, 10-15-15-8000. Checked online for this number on Google and found multiple hits related to this. Remember how long ago, when you wanted to be able to choose which long distance carrier you used each time, you had the ability to dial 10-10-ATT or 10-10-321 or whatever? This is essentially the same thing, except for the fact that they charge outrageous fees that of course aren't mentioned when you call that number. Most indicate it's a likely scam, and judging by the number of hits when sorting by date, this has been ongoing for years:
It seems there are numerous 1-800/888/877/866 numbers that lead to this same type of message mentioning 10-15-15-8000, so this isn't the only one. And while some of these 10-10 or 10-15 or whatever numbers are valid trustworthy providers, it seems 10-15-15-8000 is more likely scamming people into getting billed.
Bottom-line based on reviewing multiple reputable sites: don't call 10-15-15-8000. And if you don't find a hit here on whocalled.us for some strange unrecognized number, check Google, you'll usually get a fair number of hits.