Of course Dispatchers have the powerto hold an aircraft.
As already said, legally an aircraft needs two signatures on the loadsheet to depart - the dispatchers and the captains - if eithr or neither is happy, do not sign, so the aircraft does not go.
I would suggest at this point go back for the ops manual and latest weight / blance data on that particular aircraft, and then also get a telex from the home station for that airline to depart on any different weights.
Always cover your arse.