Reset an iPhone not possible due to Activation Lock

Hello Everyone,

I have an iPhone, that was purchased and given to an employee for the duration of the contract.

Hence I have all the proof that the device was purchased with the company funds and etc.

When the contract was terminated the phone was returned, however it is still bound to the apple account of the other person.

Communication with the other side is not an option.

I want to get control of the device we've payed for.

What is the proper way to do so?