Traffic department proxy letter issue

Hi, My sister gave me her car which is in the company name. I got all necessary documents from her. Here is my problem, I have been sent back and forth from the department because they refuse 'proxy' letter coming from my sister lawyer(two different letters). I then typed my own letter and asked them is it fine that way. Still no, I then asked how it should be written.. Again, it's a no. How does the traffic department expect me know each and every persons way of writing this letter. Each and ever person there has their own way of how they want this proxy letter to be. I am kindly asking for help please. Can the traffic department please, create their own Proxy letter that we as the people can sign.. I am tired of this running up n down, it's petrol wasted, and alot of time taken during my working hours.