In line with the DPA (Clause 10):

"Following termination of the contract, the processor shall, at the choice of the controller, delete all personal data processed on behalf of the controller and certify to the controller that it has done so, or, return all the personal data to the controller and delete existing copies unless Union or Member State law requires storage of the personal data. Until the data is deleted or returned, the processor shall continue to ensure compliance with these Clauses."