So I've done some research about this and people have said you can't use VBA to disable the context menu when you right click on shapes; it works for the cell context menu though.

I've read that it can be disabled through XML but I have no clue where to start with it...

I found this code below for XML which apparently works.

Any help would be appreciated! 

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui">
<contextMenus>
<contextMenu idMso="ContextMenuShape">

<button idMso="Cut" visible="false" />
<button idMso="Copy" visible="false" />
<gallery idMso="PasteGalleryMini" visible="false" />

<button id="MyButton" label="Excecure your macro"
insertBeforeMso="Cut" 
onAction="a" />

<menuSeparator id="MySeparator" insertBeforeMso="Cut" />
</contextMenu>
</contextMenus>
</customUI>