The "Cops are Coming" is a scam. A "Collection Agency" will allege you have a warrant for unpaid taxes, but you can cancel the warrant with a credit card. The rep will agree it's probably a mistake and they'll refund your money after your court case.
Nomorobo doesn't work with one-time spoofs. For example, scammer will spoof a number, a subscriber will report it to Nomorobo and the scammer moves on to another number. Nomorobo will block the first number but it'll just be blocking a ghost.
The numbers are spoofs of your exchange. There's 10,000 numbers on your exchange...you can't report them all. Well, you could but...
I'd get bombarded 20-30 times a month by the same number, but now I get bombarded with 20-30 one-time spoofs. Since Nomorobo launched in Oct 13, my one-time spoofs increased 125%. 275% in the past 12 months. 350% in the past 6 months. July was the worst at 425%.
Nomorobo is only good for known nuisance-numbers, but those are as obsolete as the buggy whip.