It's fairly difficult to stop robo dialers. I used to handle about a billion calls a day for providers. Robo calls had to go on separate connections and had other limits and higher prices than regulal ("conversational") calling.

But many customers would slip in lots of dialer anyways. You can tell after the fact, by looking in aggregate. But on a per call basis, nope.

Now, we tried blocking repeated caller numbers. Spammers would just switch to using random numbers. For many reasons (some good) it is simply not tractable to know if s number is s valid source for a call. It's vastly more complicated than say IP spoofing.

The most effective solution is to have an answering service/program that screens calls and allows known callers without further hassle.

Your provider could offer a service to block "known" bad numbers, but a lot of business use the same number for many things. I'd be surprised if some consumer services don't offer such services. Though, there may be some regulations that require them to attempt to complete the call.

Also note that some dialer, like political calls, are expressly allowed and don't have to follow do not call.

The best recourse you have after the fact is to make an FCC complaint and persue it. I've seen tons of complaints that go nowhere because no end user pushes the issue. For really illegal dialer, there's gonna be several intermediaries, say, 5+ isn't surprising. Each one has to escalate to the next. Without a fire under their ass, most providers will close the complaint with effectively "can't repro, dunno".