@mzanetti, are you completely sure the operator is charging for the duplicate messages? I have seen duplicates occasionally under bad network conditions, but the operator charged only one message in the end.
Also, note that when you use non-ASCII characters the message can be split and generate multiple individual SMS messages, that are in this case charged individually. The char count per SMS can drop quite a lot when doing this, see bug #1480554.
@mzanetti, are you completely sure the operator is charging for the duplicate messages? I have seen duplicates occasionally under bad network conditions, but the operator charged only one message in the end.
Also, note that when you use non-ASCII characters the message can be split and generate multiple individual SMS messages, that are in this case charged individually. The char count per SMS can drop quite a lot when doing this, see bug #1480554.