Are you trying to export contacts to your sim card from your old phone and import it to your new Xperia?
Would you be able to try to export them into sd card as sim has lots of limitations
* Some of your contact name could be to long
* Your contacts could contain multiple informations like emails, landlines, work number + mobile
Easier and trouble less option is to export it to sd card and then swap sd card to a new phone and import it from there.
If you trying to move contacts from one Xperia to another and have access to PC you could also use Xperia Companion to backup and restore your contacts.
You could also try Xperia Transfer app from Google PLAY Store.
