Any ideas why CPW might ahve charged me £16.99 DD?

The only time I have ever dealt with them was back in about April last year.

I got a contract out with them at £30 a month or so, I kept it for like 6
months and then cancelled and paid out the contract. The contract woulda
been due to finish around May this year and they stopped sending me bills
via email (they would send me emails even though I had nothing to pay)

So any ideas why they would charge me so late on? I cant remember buying
anything else from them recently (and why take it DD anyway?)