Currys delivered a cancelled order

Three weeks ago I placed an order with Currys and a day later I cancelled it. They've delivered one of the items and have also given me a full refund.

Any advice on what I should do? I don't want them chasing me for money because I cancelled and they sent it in error.

I was also going to re-order this and wanted it.

The item isn't worth very much only £15-20