I purchased a new car here it was 0% APR but in th...

I purchased a new car here it was 0% APR but in the invoiced they are charging interest. When you sign your documents be sure you read the documents and also be aware that the financial department will try to sale you extra services such as extender warranty, oil changes etc half of this services are unnecessary.
I do not understand why they do not email the documents in advance with all the additional packages to allow consumers to read this with time to allow us to make better decisions.