people abusing the information within my WHOIS, which if I remember is protected by international laws, or at least should be.
I'm pretty sure there's nothing at all to that effect. There are terms and conditions put in place by service provider companies, but at best people are bound by them as far as they are enforced. There is very little "international law"; there are treaties, which various countries incorporate (or not) into their national legislation, but I doubt there's any international treaty specifically for domain registration "whois" information.
I am receiving phone calls, spam emails, and threats.
What makes you think the spam has anything to do with you having published contact details in whois? You're doing business online, wouldn't phone calls be fairly expected if you have a company? If you aren't using specifically crafted contact details that you use only in your domain registration, how do you know that whois information is even the culprit? Threats, now that's more serious.
I do know that my information is public, but it should not be abused because of that?
This would seem to cover most of what you mention, but if no one enforces it, then there isn't a whole lot you can do about it. I'm pretty sure that text is mostly there to cover their rear, not really to meaningfully protect the customer.
Is there a way to report the people who is abusing this information? Should I actually spend my money on the private registration, even though my information is being abused and most likely recorded on their computer? What is the best way to handle this abuse of my information?
If you are receiving threats, or are being harassed, you should contact your local law enforcement and provide them with any pertient information. As for spam, that's just par for the course on the Internet these days unfortunately; I recommend installing a good spam filter and training it well.