[Q] Is it time to finally call it quits with it? (Move if need be) topic

Hey folks. Last May (wasn't with them for long) I got a Galaxy S5 on EE but due to problems with their staff I left them. (EE is UK) anyway, I have been trying to use my phone ever since on other networks (particulairy 3) but i'm getting that dreaded not registered on network message. Now I was tinkering around last night and I managed to make my phone official again by entering the Serial Number and what not on Kies via emergency recovery but still can't get past the messages. I tried downloading a official firmware to work via Odin but always seems to get the last part then fails :( (I can get a IMEI number) but I suspect my goose is cooked?