An ethical dilemma

Today I have an ethical dilemma.

I ordered a pair of shoes from a major shoe retailer the first week in December for my work Christmas party. The online tracking said they had been delivered to my office a week later.

I did not receive them. I checked with reception and our security guard, but nothing had been delivered for me. I phoned the retailer to see what had happened. This resulted in a 2 week ongoing saga - during which I had to phone them every day. It appears the courier did not get a delivery signature and they didn't know where the shoes were.

They finally issued me a refund, but would not refund the delivery charge. I was so fed up with calling them that I didn't push it and let it go.

Today, over a month later, Terry our security guard delivers me a package. Apparently they got delivered to someone in HR who has a similar name to me. I have no idea why they hadn't made it to me sooner - apart from that the other girl moved departments, so perhaps they've been sitting on a random empty desk for a month.

Herein lies the ethical dilemma. Do I keep the shoes, having only paid £3.50? Do I return the shoes? Or do I phone the retailer and inform them of the mix up with an offer to pay?

If this helps your decision, the shoes look fantastic on my feet...