Can I block my number if I'm calling an 800 toll free phone?

No, Because the network uses a legacy technology that goes back to before dawn of '800' numbers. ANI: Automatic Number Identification. This technology is what is used to accurately bill calls you make using operator assistance, and related types of calls. The scammers cannot game this information. They have no access to it in the call processing stream. One technology uses this to defend against the scammers, by forwarding their calls to an 800 number you control. Now if you can associate the call to your controlled number, with a call that is a scam, you have a billing telephone number to report to the anti spam/scam forces in your jurisdiction. This makes it easier to do TCPA lawsuits.