MTN stole my airtime

I am on an MTN Made for Me contract. My mobile data finished in the evening of 26 April 2018. As soon as I got home, I switched off my mobile data and switched on my Wifi. Thereafter I purchased airtime (R60 + R5) with my banking app with the intention to use this airtime to buy a 1GB weekly bundle for R65. My intention was to purchase this bundle the following morning (as opposed to immediately because my bundle will then expire one day later). Remember, my mobile data was switched off and my Wifi was switched on. The following morning (27 April 2018), I could not make this purchase because my airtime balance was R0.97. I did not make any phone calls or send any SMS's. Even if I did, I have sufficient minutes and SMS's which has accumulated because of my contract. This is highly annoying and frustrating. MTN, please return my airtime!!!!!