There's no guarantee that any core's can be unlocked on fused CPU's...it's really just a lottery on what you get. Some boards have found their way around these fusings, but then again some of these CPU SKU's just can't do it with these board maker's tricks employed. I could go deep here, but I just oddly refrained!
Luck of the draw dude. Dance with the one you brought or pay to play again. AMD's binning process is so wide-ranged, I wouldn't try another unit. You bought an X2 and that board with hope for more (I assume), it didn't work, and there's not much more to do there man. However, you've tried to unlock the "other two cores". Is there anything out there talking about unlocking "one of the other cores" perhaps? Hmmm? I feel the x4 on the cheap is deep-sixed, but an x3 may not be off the table at this point. (You may have a CPU destined to be an x4 but failed hard. But instead of the trashcan it went through the x3 validations. It didn't fully pass the tests but did as an x2. A weak 3rd core doesn't make it "bad" in most user's eyes and is worth looking into unlocking)