It's possible that you have exceeded the file size limit, bianca1.

If you need to import a list larger than 2MB or 1000 rows, you need to split it up into multiple imports. 

You can delete those who have been imported and upload your file one by one. 

I've added an article on how to import customer or supplier contacts for more information.

You can leave a comment if there's anything else I can do to help.