Billing issue

Why do i have to pay extra for something that is not my fault? I wanted something that cost R35 and i have to pay extra because McD is out of soda<br> Of cos i needed something to drink hence i opted for juice but my concern is why do i have to pay extra now<br> This is the 2nd time i have to suffer at Mc Donald<br> At first they only had XL not medium and i had to pay extra<br> Now they out of soda and i have to pay extra because i opted juice<br> Like seriously now? Why do i have to suffer because you guys are out of stock