Carfax won't know what wasn't reported. Obviously there was some damage and the repairs probably weren't paid for by an insurance company. Just who did it and when is probably going to be hard to find out. I personally would have a sit down talk with the dealer you bought it from before doing anything. If they are reputable they should take it back unless you signed an AS IS sale agreement but even then hidden damage like this can be a cause for them to work with you regardless of that.
Some body screwed up on the odometer but I wouldn't trust carfaxes number at all.