there has to be codes for them to know and tell you what was failed. maybe they have not much experience with these cars, which is not surprising there are few of them and they rarely fail.
There is a thread on here about Troubleshooting the OBC and DCDC converter which has a link to a picture of the viewtopic.php?f=22&t=4310&hilit=MCU+fuse#p39079
MCU and the fuse in post #2 index. This is with the entire cover removed, but it is not necessary to access the fuse.
It is very easy to check and there is no High Voltage that needs to be disconnected. Make sure the key is out of the ignition switch. Lay the rear seats forward, then In the rear trunk under the carpet is the engine compartment cover plate with 4 wingnut screws. Remove (an reinstall) in order 1-4 starting at the front left corner, right, rear left, right, then flip the lid forward on the pivot.
There you will see the OBC on the left and MCU on the right. There is a little cover plate on the MCU and the fuse is under that plate, you will need a Torx driver to remove one of the cover screws. Use a voltmeter to check first whether there is any voltage between the two buss bars on the far right, there should be none; then check for continuity across the fuse, if there is none then the fuse has blown.
Usually if the MCU fuse has blown then there is a fault in the OBC. That fuse is located in the MCU, but it's function is to protect the wiring of the OBC.