Yeah, I used mobiles.co.uk
It's a bit of an arseache, I've had to take out a new number, and then have my old contract changed to a PAYG, which takes 30 days. Once that's finished I'll then be able to get my old number on my new contract.
For the 30 days I've just been using my old SIM in my new phone, I'm therefore stuck with my old 500MB of data, but I couldn't have a different number for 30 days.
I think this is why companies are offering piss poor renewal prices tbh, because they know most will just upgrade with them to avoid the hassle, but it's not exactly fair, it's probably something a governing body should look at. Vodafone couldn't even get in the ball park price wise, they were probably 20% more expensive.