Charged twice for SMS

I sent an SMS on my Vodacom number this morning, but noticed that I was charged twice for it. I know it was under 160 characters, so I called the call centre to get clarity on why I would be billed twice. The lady was friendly but unfortunately couldn't give me any more info than I already see on my Vodcom profile online. She sees two SMSes sent to the same number 5 seconds apart (which is not possible - I wouldn't be able to send an SMS twice in such close succession on my Nokia E5 phone). She cannot verify that indeed the SMS was under the 160 characters - I've gone back and counted and it's actually 132 characters.<br> <br> I would like my airtime to please be refunded for the SMS I was erroneously charged for.