I'd like to explain a bit about the reason for this, and the thoughts behind it. Please know that I'm about to say a lot of things that may not be relevant to you. It isn't necessarily that crypto is against our terms of service in itself, it's that hogging shared resources for extended periods of time on our standard droplets is considered to be abusive behavior.
You see, we can't rightly put in our terms of service every way that someone can abuse server resources. This is a constantly moving target, and it would severely confuse customers who would then be required to continually check the list for updates. Instead, it makes more sense that we focus on what it is that makes the things that would be on that list bad. What it really would come down to would be just what I said above, hogging shared resources for extensive periods of time.
A side note to that is we do specifically forbid coin mining on some of our promotions, and we state that up front. If you ever find yourself on a promotion for $100/60 days, that promotion does come with that extra stipulation.
Given that we allow customers to spin up resources and then pay for them at the end of each month, it isn't entirely uncommon to see someone pop in with a stolen credit card, spin up the maximum amount of droplets, blast shared resources, and then skip out on the bill. Obviously our business strategy opens us up to things like that, and it's our burden to prevent (which we work very hard to do).
Now, I'm not at all accusing you of any of that. I recognize this post as one that is going to be read many times by people other than yourself, and I know that my reply answers a lot of questions that are going to be asked in comments over the next X years. For that reason, I have expanded well beyond what is relevant to you specifically, and I have sought to answer many other questions ahead of time.
With all of that out of the way, I'd like to move to your specific scenario. When we say that you're CPU mining and shut you down, it's because your usage looks identical to that. Admittedly there may be some very rare situations in which a different kind of activity looks like CPU mining. We haven't run into this enough to justify stopping to ask the question first, to be frank. Hogging shared CPU degrades performance for other customers, so the absolutely vital thing that we do immediately when we identify this is to shutdown the user who is causing the issue. There may be multiple other customers who are unable to perform at a reasonable baseline due to this.
If you do need to blast the CPU for long periods of time, we have a path for this. We have dedicated CPU threads available with our Optimized Droplets. You can take a look at those here on the Compute tab: https://www.digitalocean.com/pricing/
If you can promise me that you'll move this workload over to our Optimized Droplets, I'll override the previous decision and unlock your account. I'll also toss a credit your way for your trouble.