Can a new Property Manager change the rent amount mid-contract?

Good morning,

We have a leaseback in Divonne les Bains. It was sold by Vacances Bleue to a new company, Adonis. Now Adonis wants to change the rents paid, claiming that they found addiitonal expenses that they did not know about and that this is the low season for bookings for the units. The contract was renewed by Vacances Bleues in 2018 for 12 more years, expiring 2030. Can Adonis arbitrarily change the rents that will be paid to owners? If this is not allowed under contract, what are effective ways to ensure Adonis continues to pay rents by the contractual obligation? Thank you.