Take it to a truck shop..almost any semi-trailer repair shop should be able to fix this. You might have to buy the new 7 way RV plug at a big box store or auto parts store, then drive into a truck repair facility (not a truck stop) and smile, show them the new plug, and the damaged one on the trailer, and they should have you going in under a half hour.
What you are looking for is a guy (or gal) who will just cut the old plug off, and wire on the new plug, playing attention to the color codes. This is assuming you have plenty of cable, enough that you can cut several inches off and still reach the plug without strain when turning.
Be sure to test all functions after the job is done, before you leave the lot.