I'm having the same problem. My contract ended with ee a week ago. I got a sim only contract instead, with tesco mobile. Everything's been fine,however my phone broke today. So I've used my previous contract phone, but it's locked to ee. Try using the unlock form online but I get the same message as you.
I desperately need this fixed as I now have no phone/no one can contact me. Current phone is broke, and I don't have a sim that works with my old phone unless ee unlock it
