Apple isn't Helping to Get iPad Ownership Back from an Employee

we have purchased an Apple iPad for our company and one of our co-workers was using it for business purposes. after he has left our company he returned the tablet but claimed he doesn't remember the id and password he used to find my phone. we have reached apple turkey for couple of times providing the necessary documents like invoice, tax id and the credit card statement which we used to purchase the iPad, but still apple refuses our ownership. even we had used our official company contact number and company email to contact them. we do not know what else to do and Apple company is not willing to solve our case.