R50 airtime got finished in 30 sec before I use

I bought R50 airtime at 20h22 which I wanted to switch for data bundles so I can use my whatsapp, however at 20h31 my airtime was already finished. I called the call centre to find out if I have subscribed to any company and (Prudence) said no and it doesnt show any subscribtions except for internet usage. I told her I have switched off my data and how can my airtime just vanish like that??? this is really inconveniencing for me as I had plans for the airtime. It is not the first time I am experiencing this and I was told switch of my data. I told the call centre agent that I am using this phone for 4 years and i never had this problem before.<br> Can someone please have a look and get back to me. <br> <br> Regards<br> Lebo