Bercy and Accor Arena are just the same hall, but with a different name. When it got opened in I believe 1984 it was called Palais Omnisport de Paris-Bercy, but people were simply calling it Bercy because the name is to long and the quarter around it is called Bercy as well . Than around 2012 or 2014 it got closed to get renovated and the seating being moved from 17.000 to 20.000 and the name of the hall being changed into Paris-Arena. Than you got a hotel that bought name which made it being changed into AccorHotels Arena and a few years later being shortened to AccorArena. However most people keep calling it Bercy due to the long history of sports (basketball, handball, tennis and boxing matches) and music being connected to its name.
You compare the situation to U-Arena. When it got opened it had the name U-Arena only to be changed into Paris La Defense Arena in 2018, due to a company buying the name. But people keep calling it U-Arena. Now another company has bought and changed it into Plenitude Arena