You're not a mug, you've an honest person treated badly by an incompetent company.
You would be a mug if you dealt with them again ;-)
Don't be surprised if you haven't heard the end of it. They might well lose the item and then attack you again. If that happens, do not waste any more time or money on them.
I would have notified them, too, and have done similar in the past. Amazon botched initial delivery of a $500 item, then sent a new one, but both eventually arrived. I called back and they thanked me and emailed me a shipping label and instructions that gave me weeks to get it done.
So I'm down another day's income, and honestly starting to feel like a bit of a mug given the responses here.