I earned the coin but I cannot reunited with the other people?????

Have you seen the House of Parliament and The Betrayer's Price on one side and turned it around to see St. Paul's Cathedral? Beware of saving in closeup views, there was a glitch that corrupted exit points and the follow-up location. That could have happened here. If you did save in a close-up view, fall back to an older savegame.

It's also possible you're missing something, but don't know what it could be. Open the Progress window by pressing P and check which quest shows which amount of points. This info might help tracking down if there's something.

Further on the game's travel map the location names are color coded:
- golden => Here's something to do to progress in the main story (but maybe you have to do something else elsewhere first)
- silver => Here's something to do to complete optional bonus tasks
- grayed out => Here's nothing to do, disregard this location for now.

thanks for your tips. I uninstalled it, but when I play it again I will know what to do. Thanks a lot.