Paygate won't process online card payments.

I shop a fair bit online, always with a card which I keep specifically for online (so if a problem occurs then it won't affect my other cards - which are with another bank). However, Paygate won't accept my online card (6 times now over the past year it's failed to accept) but if I go to another site like amazon - my card payment works fine. Twice I did an EFT with paygate to get the purchase - but now I had enough and won't buy from sites with Paygate anymore. I've recently cancelled my Takealot account because of this.