Silent Spam Calls to toll free numbers

I am getting a single call almost daily from all over the US and they leave a message that sounds like pocketdial, no voices, that lasts exactly 3min, which is the timeout on my voicemail.   If they do this daily it will cost me 4.50 per month, but my provider will charge 9.00 to add an autoattendant, which I don't actually want because it is a direct line to me.   My autoattendant would have to say "dial 1 for Heather" and nothing else, stupid!    This is terrible and someone needs to do something about it, but I don't know who or how.

I have been getting the same calls.
I have call blocker, but I block one and three new numbers call in... all the calls are mostly from Canada.
I don't know what to do.

I was able to stop lots of calls to my 800 numbers with a system used with my Ring Central account... it allows me to block entire area codes and single numbers too.
It's not the best but is helping me out a lot.

Comcast allows us to block, I believe it's 10 or 12 numbers within a "rule." We keep getting the Google pushers that you can't return calls to, and occasionally still get a [location] Office of Economic Management wondering if we found a place to move to. What are they getting out of that?

I can't say this enough times...get a challenge-response type call blocker.  No criminal telemarketer spam calls get through.  None.  The phone doesn't ring...not even once.  The caller is instructed to dial a specific number sequence, hang up, and call back.  This places them in the whiltelist, and when they call back, the call goes through as normal.  In four years of use, I've not had a single telemarketer criminal dial through.  Not one single time.  My land line belongs to *me* again, not the scum-bag criminals.  It's life-changing.  The site TOS prohibits me from naming the device.

GregAtTheBeach,
Can you describe what the box looks like, without naming it?  Single- or multi-line device, white color, LCD display, approximate cost, other features, number of syllables in the company name, etc.?

Did your response get blocked by the site Admin?

Yeah.  I've tried before, with "sounds like" etc. Was blocked.  Let me try again: It's seventy nine dollars even, and is version three point one. On that big on-line retailer that initially was all about books when they started.  The Bezos one.

Thank you, GATB (even a year later--I forgot to look back here). It's too bad that even in the Forum areas (where we are *supposed* to be able to talk about call blockers), there really isn't anything helpful.