Well, here's one message of sympathy. I have no doubt it can be galling to have this happen.
If the Office application is on a recovery disc, then he's probably right, you can't install it again. But if it's an actual Office disc then as far as I'm aware the terms of the EULA are that you can only install it on one PC at a time, which since you no longer have the original PC may be OK.
As for the original. Have you contacted the courier to see if it ever got to Multivision? If it didn't then it may be in their warehousing somewhere. If it did, assuming the Administrators have been called in, then contact them and ask for your PC back. It is not Multivision property and as such cannot be included in any collateral for recouping bad debt. If they have just closed down with no Administrators then you probably may never see that PC again.
Wish it could be better news