How to solve wrong spreadsheet export xml

I have a form that receives some registration and is transmitted to another page via ajax that does the insertion in the database. The problem is that at the time of receiving, if I do not use utf8-decode on the variable where it has accent will lose formatting inside the database. So far so good, the same problem begins at the time of exporting this data by phpmyadmin. Whenever I try to export it it loses the formatting and I did not find any combination that works.