Flat cooldrinks

I bought a case of cool drinks at Makro only to get home and find out that they are flat,they seem to be sealed but for some reason they are flat,I stay very far from Makro which will cost me double the price of the cool drinks to take them back.i called coca cola just to understand what could have caused the drink to be flat yet it seems to be sealed and answer I got was taken it back to Makro,this not the first time iv had problems with coca cola or maybe it's a sign I should stop being loyal to them