for anyone reading this for information in the future, always go for O2 over Vodafone. They accept cancels within 14day cool down period like they should. Had two phones from CPW with £100 off with a 12m O2 sim and then cancelled the sim immediately. Happy days.
Just an update my chip was cancelled. I just called again no need for an excuse they are already aware of the CPW deal so just say that you only need the phone so your cancelling within the 14 day cooling period.
They have upped the price - now it's 209 plus the vodafone 15.5.
Being able to cancel SIM within cooling period is a consumer right. There should not be luck and patience needed here. Vodafone is simply peddling lies on CS and asking people to go to CPW instead while the actual SIM only contract is with Vodafone. This a non deal as "luck" or "lottery" is needed for it to work.
For anyone struggling to get Vodafone to cancel I'd suggest using their online chat or simply hanging up to try another advisor. It's a bit of a lottery but trying at different times may help. If you do so within the first 14 days you should be able to get avoid being charged the £15.50 fee (which is only chargeable after 1 month with Vodafone and not at point of sale). Patience and persistence needed.