Data lost upon conversion to contract

Good Day<br> <br> After numerous attempts, I recently ported my number to Vodacom and became a Prepaid customer. I bought 1 Gig data on Sunday, 15 February 2015 with an expiry date of 14 March 2015. I signed a Vodacom contract on Monday, 16 February 2015 and as a result I lost the data I paid for the previous day as well as the airtime that remained. Please can you explain why the data was lost or why a credit to my account could not be made for the value of unused data and airtime?<br> <br> Regards