Are you sure it wasn't a mate of a mate winding you up?

I'd make the observation that if a porn rental 'store' was trying to rip you off with a clones SIM, then you'd certainly notice it. I'd also question why such a place would give a cloned number for incoming calls? Since Orange don't charge for incoming calls, it would make no sense. The only way that I could see that occurring as part of such a rip of is if the 'store' made an outgoing call to their customers mobile phone - and the number was then stored in the address book.

Either that, or your number is identical to one with a similar area code that *is* a porn shop and someone printed up a bad batch of cards at some point and hasn't realised.