Nedbank Credit Card limit increase without my permission.

I have a credit card with Nedbank. I have asked them to decrease the limit to R15 000. Which they have done. My limit has increased once again without my permission to R26 000.00 Every time Nedbank phones me to increase my credit, I decline. But they still put it up with a R2000 here and a R4000 there. I use the funds without even realizing it has been increased. This is really not on.