Mtn ****ed me

On the 17 June around 23: 00 hours ive bought R499(200g) voucher on mtn super deals. through my capitec app. I check the balance till i went to sleep. Now i check the balance again theres no data. I called the customer care line they say ive changed plan and loose .y R500 data. How is that possible. Where did i charge that plan. Mtn must bring back my R500.