Ipad hacked ICloud

My company has bough 14 ipads to using as the digital menu for the customer.unfortunately that 2 week ago one has been lost but all the iPad has the same iCloud some how somebody was hacked them all now i can access to each of the device more worse that the iCloud account also changed.now i can't do anything because if i open the wifi all of them will lock.is there any way to fix it? because the company bough that one by hand carry ,there is no official receipt from Apple but the box still have.