An asshole ex-client who owes me in excess of $1000, and doesn't intend to pay, has left me on their Twilio administration (unknowingly clearly) panel. I have the option of requesting around 30+ Cayman Islands numbers to auto charge his card enough to offset the debt.

Hmmmm.

I'm going to test the waters, and purchase 5 numbers to see if it can get back to me.
From what I've explored on the dashboard, it doesn't show you who purchased the numbers.
I feel like I should have an alibi ready soon. >_<
This is stressful.

Exploit it slowly.
Keep the credentials and - what is a Twilio?? - buy stuff to yourself or your business/clients in small amounts.
Maybe find some previous, recurring transactions to mask yours.
Profit.

People call me evil, but they just don't get it.
</self-mockery>

Hahaha, that's quite a plan.
Twilio is a cloud telephony provider. Basically you can purchase numbers and programmatically make calls, or push out SMS's etc.

I'm sure they'll discover it soon enough (or once they get some competent devs back on the force, who know a thing or two about managing access on production accounts). I just want him to wake up with the shocker of a nice fat amount charged to his card.

Use it to blow up his phone and his clients phones. Talking about how he screws people he owes money to. If he done this to you he has probably done it to alot more.

Not paying is the crime. Destroy his production setup (a voice message with "This call will not be forward because {{name}} does not pay his/her bills. Do not contact us again..."). And tell him to pay you or else he will find or what you can really do.
I take it you already did give the client a few notices. You can take legal action by putting an agency on it.

A cool 25 toll free numbers, and $750 later, I got bored, and subsequently the access was quietly removed.

He didn't even drop me an email. xP

Revenge justified by non-automated access mechanisms is fun. :)

@hjk101 I'm actually not sure what to do in cases where the contract is not honoured, but the amount isn't too high.
As a matter of principle I want to pursue legal recourse, but with such a low value there's just more losses to be made in the bigger picture.

Having said that, the above are the sort of things I then look for. Given such folks usually have little understanding of how critical a tech lead is to their nascent early stage architecture, it's easy to fuck them up just enough to teach them not to repeat this down the line.

I'm of two minds about revenge opportunities like that.
On the one hand "two wrongs don't make one right" is a guideline that has been working well for me. On the other hand, the legal route is fine and all... but some people don't learn unless they get a kick to the balls.

@VaderNT I completely agree. It was excruciatingly painful to purchase that first number, and my heart didn't stop having a spasm until an hour later.

Yet, overall, nothing changed. I still hate the guy, he's still not paid me squat, and now I just feel a bit guilty about having done something ethically fuzzy. :/