VW didnt give me my radio pin and now want to charge me for it

My car was bought from Mccarthy Volkswagen Waterkloof Glen in Pta. My battery ran flat and my radio is asking for a pin, when buying the car they were supposed to give the radio pin in the book, i have the book with me which hasn't been filled in due to incompetence or negligence. I live in Rustenburg and im not willing to pay for their unprofessional service. They say i will be charged R750 for "losing" the pin, but something can only be lost if it was given in the first place. I have the book as proof that it was never filled in. I called the dealership and spoke to 2 people who say they cant assist. Please assist.