Unnecessarily charged extra due to inaccurate equipment

Sent a package from Cape Town to my folks in Mpumalanga. Measured the box and paid the quoted fee. Their Johannesburg scanning machine said my measurements are incorrect and they charged me an extra R138 for a larger size. It was eventually delivered in good time but we measured it again and it is definitely not as large as their scanner says. I feel ******** out of this extra amount because of inaccuracies in their equipment. I can't get any help from them either since they fail to understand the simple comment I left.