Loosing emailed documents

On the 10th of November I asked to have my surname changed on my account. After emailing through all the requested documents, I received a response on the 12/11/2015 stating that all docs was received and my details have been updated. Upon receiving my new account in December, it was still on my old surname. When I queried this, all response that I am getting is that they don't have the documents needed, and I need to send them in again. How can they tell me everything was changed, and now all of a sudden they don't have my documents??? I needed this to be changed ASAP as I need this account as proof of address! <br> This level of client service is unacceptable!