Seems the smart idea is to wait for the S7 realease and benifit from the S6 price drop.
Had an offer from 3 of £29 monthly (24 Month contract) 1GB + Unlimited text/mins so happy to wait a few weeks on that, also whilst browsing I considered the 64GB phone rather than 32GB, they wanted an extra £9 a month.

That was to upgrade from the "The one account" currently being sim only and on a booster with my wifi for £15 that ends this month (Compulsary as they wont keep it active any more)
Also managed to to get the phone working again, I thought it was a password issue but it seems a different battery sorted it, so I put the hammer and tool box away.

Also, after handing my phone to a teenager to look at my S4 is now working properly, we tested the sim in his phone and it msg'd some setting for access, so he twiddled with the settings on mine and all works well.
O2 upped my contrast from £16.21 (sim only) for 2GB unlimeted Text/calls to £21.76, after a few calls I now have a £15 12 Month contract (som only) 3GB Unlimited Text/mins and happy to keep S4 now its works ok.