"paid the associated duty for the upgrade (my credit card was charged)." I'm a little confused by this. I wasn't aware an additional fee/tax was collected for use of SWUs. Are you sure you didn't request a mileage upgrade and a service charge wasn't collected?

In any case, use of the SWUs to Europe will take some detective work. CO only allocates a few (if any) seats during busy times/destinations. London's a prime business travel destination. CO would rather sell the seat at full fare than give it to a economy fare purchaser.

THe info you got was flat wrong unless the info provider misunderstood you and thought you were asking about complimentary upgrades.

The SWUs you have now are very valuable (no fare class restictions). Available SWU-eligible seats and the dates you'd rather fly will almost never coincidentally occur.