The Courier Guy double charges for package half the quoted size

When it comes to customer relations The Courier Guy has no Idea. I spend thousands at this company every year and often have hiccups but this last one takes the cake and the way i was dealt with by Mpo was disgusting. They charge by volume and not by weight. They collected a 25kg package for me and on their website they say that if it's more than 17 kgs it must be broken into 2 for easier handling. I paid for 25cm x 25cm x 180cm but my package was actually only 25cm x 12cm so only half the volume I paid for. So I was hell of a surprised when they sent me an invoice for an additional amount which was double what I had originally paid. Their excuse is that they collected 2 packages, the website says to break the package down it doesn't mention that it will now be 2 seperate delivery charges. There was no negotiating with Mpo she was rude and arrogant and slammed the phone down in my ear when I asked to speak to someone in their legal department.