Why did you put "BUG" in all caps in the title? You aren't posting a bug report, and this isn't the bug report forum.
Now as to your question, probably the easiest thing to do would be to edit the save (after making a backup!). That said, I think the larger question is why did the AI make 200+ of the exact same convoy? It won't do any good to delete them if the AI is just going to create 200+ more of them. Do you know how it happened and have already dealt with that problem? If not, can you give us more details so we can help you figure out how to avoid a recurrence?