rotten bolt is stuck in the engine cover

[scorpioy]

Hi, I have the e70 diesel and am trying to replace the glow plugs.
But I got stuck at the early stage of this. A rotten bolt is stuck in the engine cover and prevent me to remove the cover alone with the sound proofing foam block. Anyone can tell me some idea how to deal with this? Thanks.

The 1st picture with part 9 shows the bolt.
The 2nd picture shows my car's actual bolt. The inner hex edges are gone.
The 3rd picture shows the engine bay, where I tried to stick a hex head and turn it but it's not loosing the bolt.