OT: A plea for help

We have a problem.
Some company has spoofed our telephone number for their caller ID, and have been calling up people harassing and threatening them. We get calls from many very pissed off people, and I have to explain the situation to them.
Usually its one per week. We took 5-6 calls about this, just today.
Gotta stop this. The folks doing this are dragging our name through the mud every time they do this, as they are misrepresenting themselves as us by using our phone number.
We filed an FTC complaint, but as usual, the technology the felons are using exceeds the ability of the regulatory agencies to do anything more than say “huh?”.
My best guess is that they are scammers, seeking personal identifying info.
I would like to take them down. In a seriously big way I want to take them down.
I have nothing to work with at this moment. Just an 800-ish number. I’ve tried calling it, and speaking to people there, but we cannot get any info out of them.
Since I don’t want to break the law in defending my company against them, I need to find legal mechanisms to disrupt them. And more specifically, I want to identify them. Our lawyer has marching orders to make their life very painful (including filing police criminal activity complaints) once we have enough info to find them. So we are now trying to find them.
This is where I need help.
I don’t know if it is at all possible to track usage of a particular caller ID by any phone exchanges. Or if we can call the number and back trace to a location. Or locate a provider by their 800 number.
I’d like to be able to do this.
I’d like to avoid changing our phone number, which is the “simple” solution. I’d like to see these jokers taken down. Any hints or guidance on this? Is this something a distributed group of motivated folks could do? Wouldn’t it be nice to cause them some serious headaches?
Thats the problem these days with all these scammers. There is no real cost to their scamming. I’d like to alter the equation so that scamming online like they are doing comes at a very high cost.
Open to advice/ideas. DDoS is out. Collateral damage is unacceptable.
Maybe its time for an SPF-like thing for VOIP/telephones?