Recurring data

Dear Sir/Madam. I have a few amounts of 20gig recurring data added to my account, which adds up to thousands of rands. I'm told its self service but every time I ask the operator on 808 or I go to the MTN shop to ask the operator to show me how could I have bought such amounts of data because trying all the options only allow me to purchase 3 gigs of data. My sim is in my Ipad, which I only use at home and only on wifi and it has a password so i'm the only one using it and I didn't purchase such data. Maybe you can explain to me how to buy 20 gigs of data because I didn't buy it and not the 808 or the MTN shop operator can show me how it is possible to purchase such huge amounts.<br>