Charged for a service they are not providing

I joined discovery insure with the fuel back benefit. I was told to sms my card numbe to the number provided, which I did. Something happened on discovery’s side and the card was not linked correctly therefore I did not receive any fuel money back. Discovery refuse to take responsibility for their system not linking the card correctly. On top of that now after folllow up calls to try ensure this card is linked correctly when I swipe it at the petrol station only some of the transactions go through to discovery insure. When I complained to discovery they said it is the customer responsibility to check. NO discovery insure when you charge for a service it is your responsibility to have a system that works so the client gets that service. Discovery should fix their system and take responsibility for the glitches in the system, don’t turn it back in the customer.