Bank card issues

On Friday morning I filled up my car at Godrich Shell in Bronkhorstspruit, like I do at least once a week.For the third time in the last two months I get told that my cheque card is declined by the bank. I say to the attendant that I know there is money in my account and it is not the first time that this happened. He gets upset with me. I get out of my car (I am a disabled person and this is a pain already) I go inside the shop and I draw money at the bank teller using the same card, pin and account. I pay for my fuel. This is now the third time this has append to me and it has also happened to my wife. In my wife's case she had to stand in the queue for a long time, and also draw money from the same account, same card. Either the attendants are fooling around or the card machines are not working. Please fix this, as it is a huge pain and also creates congestion at the garage and teller.