VODACOM ROBS AGAIN

I have been a Vodacom client for more than 20 years, I went over to prepaid and VODACOM basically stole my remaining airtime just over R300.00 worth ON 30 March 2018 THAT I PAID FOR!!!! No where in my contract does it say that this will happen should I convert my contract to prepaid and I was not told this when I informed them of converting my contract to prepaid - if I had known I would have used up all my airtime. THIS IS DAY LIGHT ******* AND TOTALLY *********! Time to switch providers who are cheaper in airtime & data and are not so arrogant!!!! TOTALLY ****ED OFF!!!!