Unlock Iphone From ID Mobile

After a bit of advice if poss. My iPhone contract with ID Mobile expires next month, so I phoned up to either cancel it or go for one of their SIM only deals. I asked them to unlock it to any network and they said they can do this but it will take six months from today. I then asked them to change my contract to a SIM only deal and they said that this isn't possible - in order to do this I have to cancel my contract and then take out a completely new one with them. So I asked to cancel my contract and they gave me a PAC code, which I need to use to keep my number. However, they said if I take out another contract with them I can't use the PAC code, and that I will have to have a new telephone number, which I really don't want to do as I've had the same number for 15 years. So now I'm in a situation where I can't move to a different provider because my phone is locked to them, and if I want to keep the same number I have to keep paying them £37 a month for the next six months until they have unlocked my phone. Anybody else come up against anything similar? Is there any other way I can get my phone unlocked? Sorry for drivelling on and possibly making little or no sense, I'm just feeling quite frustrated after just having spoken to them!