They can't refuse a shortcut; they can merely shorten it by naming a place where they will deviate from the shortcut. The game then advances to that point, and they must take a different action than the shortcut.
716.2b Each other player, in turn order starting after the player who suggested the shortcut, may either accept the proposed sequence, or shorten it by naming a place where he or she will make a game choice that’s different than what’s been proposed. (The player doesn’t need to specify at this time what the new choice will be.) This place becomes the new ending point of the proposed sequence.
716.2c Once the last player has either accepted or shortened the shortcut proposal, the shortcut is taken. The game advances to the last proposed ending point, with all game choices contained in the shortcut proposal having been taken. If the shortcut was shortened from the original proposal, the player who now has priority must make a different game choice than what was originally proposed for that player.
What you should do: After your opponent refuses the shortcut, ask at what point of the shortcut they would like to do something different. If they refuse to name one, call for a judge as they are refusing to take a mandatory action. If they name one, they gain priority. If they don't do anything different than your shortcut had proposed, call for a judge as they just violated 716.2c.
- Obviously, they can refuse a shortcut if it's illegal. For example, they could refuse the shortcut by pointing a point at which the complete game state would no longer be known