Is it possible to block a contact on the iphone so they can't SMS or ring me? Or do I have to do it through my provider?

Not sure. I’d just tell’em to fuggoff, lol.

Just set up a personalised response that doesn’t use a ringtone, or that silences the ringtone.

They have deliberately set-up numbers for girls to give out to guys who pester them when they are out socialising. The message says something like: “If you have arrived here – it is because the person who gave you the number does not wish to speak to you.” You could find one of those and in the personalised setup have your annoying number divert to it.

Try Google Voice. There might be something there for you.