Accountant overstepping their reach

An accounting firm that we did not choose but was handed over to when previous accountant retired. New accounting firm had been pressuring us into making them an Online Administrator.

When they were told No thats not necessary over and over again just let me know the details & I will Invite. Found out today somehow they managed to go over our head with MYOB without our permission and are now listed as an owner. How the hell did MYOB let them take control of our business like that???