Kenwood A901d?

Hi,

Can someone please help. The bit of machine where you fit the attachments into, the planet shaft has an attachment fitted into it and we cannot remove it. Have tried oiling it, freezing it, brute force etc etc but nothing works. Any idea where we can buy a new part? Is there any reason why this happened. I bought the machine and the attachments separately, perhaps the attachments are the wrong size.