Sounds very much that they didn't repair it right, then, and perhaps the camera has some more serious issue. If they had repaired it right the first time, then when they got the camera for the 2nd and for sure the 3rd time, they should have just checked it and concluded there is nothing wrong with it. I have seen such reports as well, and if that were the case, I would have advised you to check the focus and your lenses more carefully. But if they actually did perform a repair the 2nd and 3rd time around, it would mean there really was an issue with their own previous repair attempts.
Anyway, I hope you get it resolved and a replacement. I would not accept a 4th attempt in this case.