Refusing to re-imburse money

I have 2 data contracts with MTN for more than 7 years, been their customer more than 11years, 1 day ago I ran out of data on my contract d whilst rying to top up, I mistakenly bought 3gb+3gb night for R199, I honestly misread it because as Im shocked there are such prices for very little data, so a had to buy another 20gb for same amount, when I phone d asked if I could be reimbursed they said no, Wow what a **************** of a very loyal customer.