The post is clearly undersized, and the seat lug ears are bent in. The slot edges should be parallel.

The correct solution is to take it to a well equipped bike shop, and have them spread the seat lug ears back out. That should be followed up by reaming with the correct size seat tube reamer to clean up the inevitable distortion. It would help if they have a seatpost sizing gauge, but a variety of seatposts in the junk bin will also work. If the bike is SL, it should be 27.2.

Campagnolo seatpost bolts are very small for the job they do, and it only works when everything is set up correctly and precisely. If you don't, the bolts will break. There's a reason old PX10's and what not had big honking seatpost bolts. They needed them to deal with the typical sloppy fit.