I have no idea who you are or who you bought the block off of, and I certainly don't want to step on anyone's toes here. But if what you say, is true, then someone is screwing you around. What can you do is a good question. I have no idea! I guess things on this forum (as with other forums) are sold pretty much on the honor system. And that means buyer beware! I bought from a couple members on here and they were truthful guys, shipped fast, product just as described and I would buy from them with confidence again in a heartbeat, Great guys.
I hear these horror stories like yours and I DO hesitate to purchase from guys I don't know. I consider myself a very truthful guy when dealing with others and expect the same. Most guys on here don't like to sell on eBay, many would rather sell here, under the radar and avoid the fees. But eBay has buyer protection and that means eBay won't let this type problem go uncorrected.
I am still looking for a junk or lonely C8,C9 or D0VE head for practice porting, and would pay what some guys on here ask for one plus shipping. But how dose one keep from being screwed, like you apparently were? I don't know!
Best advice is buy from guys on here with a good rep as a stand-up member, or buy from local members. And if all else fails after buying from a nearby member and getting screwed, put a 1/2 inch ratchet in your back pocket and have a face to face with them. Money back or teeth laying on the floor like someone spilled a GD box of pink chicklets. And I expect the same for screwing ANYONE over!!!!! Sorry guy, I don't know what else to say.