Sure you have coverage in your area? Also, that 15+15 gig deal is once again a 2 year contract. I will repeat myself again, avoid 2 year contracts if you can, cheap in the beginning but 90% of the time more expensive in the long term. Also, the ability to leave a company due to bad service is an extremely valuable deal.
It seems like it's not 2 year, you can get it on a month to month contract as long as you don't need a device and get it sim free.
Definitely want to steer clear of 2 year deals.
http://www.telkommobile.co.za/plans/plan/smartinternet-15gb-promo-0/months/1/