I'm not quite understanding this. It could very well be my fault, not yours.
What I think I see...You took off a hitch to install the OEM bumper and you're putting the hitch back on.
Are your broken bolts for the hitch, not the bumper? My OEM bumper doesn't bolt into the frame. It has studs from the bumper with nuts where MaloStapalo's picture has two bolt heads holding an aftermarket bumper.
The nuts that go inside the frame for the hitch on mine were attached to a 1/2" x 4" piece of sheetmetal. I'm sure there's a name for those but I can't remember it and failed to find it searching.