No limit increases for Credit card holders ever

So I have been a discovery card holder for over a year now, i have never missed a payment and twice my card was paid up full. Last week i contacted Discovery requesting a limit increase on my credit card. I was told to contact FNB , i called FNB and was told to call Discovery, i than called Discovery again only to be told that Discovery cant not increase a limit on a credit card and the limit that was initially given to me is one that will remain forever . How is that possible that what is the purpose of having a credit card? Is this true Discovery ? Or was a just speaking to someone who didnt not have a clue about your products?