How to contact HMRC for over claimed Gift Aid

I represent a charity, and I think we claimed Gift Aid for a tax twice, and the HMRC paid us each time. What is the process of contacting HMRC to send the money back if, indeed, they paid us twice?

Hi RMS,
You would need to contact the Charities office.
Charities and Community Amateur Sports Clubs                                                                                                                                                                                             
Charities Savings and International 2
HMRC
BX9 1BU
Thank you. 

Thank you. I had to call HMRC on 0300 123 1073 to get help. I just hoped that there would be an online option.