Don’t panic. Take a look at https://oysterfares.com/refunds-of-5-oyster-card-fee/ which is under Latest News. You’ve got six months to collect the refund automatically. Note though that a single bus journey will not actually work, you’ll need to make a second one a while later to actually pick up the refund. Half an hour should be enough.
The helpdesk may be able to tell you when the other card was purchased, depending on whether it was registered by your friend or not.
Hope this helps.