Poor service at nissan

My wife took my np200 which is still under warranty to nissan gezina.The car was making funny noise when it was starting & always resseted the kilo & clock on the cluster.The lady who helped her made her sign a form she did not understand.I just wanted them (nissan gezina) to check what's wrong with the car since it was under warranty but at the end of the day I paid R1057 for a fuse replacement.What really ****ed me off was they did the work without my permission.The lady at nissan said my wife gave her permission by signing the form which was written in english & afrikaans only & was not explained to her in her mother tounge so she(my wife) could understand what she was signing.How was I suppose to pay for diagnoses when the car is still under warranty?How was suppose to know what is wrong with the car if I did not take it to the workshop?Can nissan gezina get someone who speaks sepedi or zulu to explain what the people are signing,Why do you work on a car without the owners permission & expect the owner to pay.How do you charge a person R1000 for a fuse?