2023 Peugeot Rifter Fuel Efficiency Issue After Software Update

I purchased a 2023 Peugeot Rifter from the Ankara ABC dealership. Previously, my vehicle could travel 750 km on a full tank, but the ABC dealership called me and said an update needed to be performed. After the update, my car has only been able to go 600-625 km on a full tank.
Despite reporting this issue to the service center, they claim there is nothing wrong with the vehicle. I am experiencing significant distress due to this situation. My Rifter's fuel efficiency has decreased noticeably after the software update at the ABC dealership, and they are not taking responsibility or addressing the problem.
I request that the ABC dealership investigate this issue thoroughly and either restore my vehicle's original fuel efficiency or provide a suitable resolution. As a customer, I expect better service and support from Peugeot and its authorized dealers. This experience has been very disappointing.