Obligations of the controller in case when the data subject request is unadopted
If the controller does not take action on the request of the data subject, the controller shall inform the data subject without delay and at the latest within one month of receipt of the request of the reasons for not taking action and on the possibility of lodging a complaint with a supervisory authority and seeking a judicial remedy.
Chapter III, Section 1, Article 12, Paragraph 4
Regulation's subject matter
Transparent information, communication and modalities for the exercise of the rights of the data subject (Article 12, Section 1, Chapter III)