Telkom spend ****

I recently upgraded my phone and the service at the store was really good but I see without my permission they increase my spending limit from R1 to R1500. For those who don't know this is a credit limit that you can use to buy data or if you make a phone call and you don't have any minutes it gets deducted from that amount and at the end of the month they debit what you have used with your contract fee. I was never once told that this amount will be increased and also I never signed saying I want it increased.