reporting a phone as lost sounds sensible - but can have unintended consrquences

A few weeks ago I thought I'd lost my LG G2. After looking for it I decided to ring Three to stop the sim card being used- in case someone found my phone and popped out the sim card. I was surprised when Three said they could block the phone as well- even though it wasn't a Three phone. Apparently the phone's IMEI number is sent to Three when used with a Three sim card- even if it's not a Three phone. I have 'lookout' installed which should do the same as apple's iphone tracking software- allowing me to remotely wipe and track my phone- however, despite being able to log into Lookout's site - it came up with an error when I tried to locate my phone (whenever I've tried the same thing with an iphone in the past it's worked perfectly, as did the Z1 compact preinstalled tracking software- it's something worth testing before you think you've lost your phone!). So, I rest all my passwords- gmail, hotmail, facebook ...   ...  and the next day I found my phone - and rang Three to stop my phone from being blocked (though I did have to get a new sim card). I carried on using my LG G2 happily on Three & O2.

Roll on a few weeks- I'm now using the LG Flex (gets better the more I use it!)- and so decided to sell my LG G2. I've used Phone Show Forum, eBay and Gumtree for selling/swapping phones. This time for speed and because I wanted to swap for something I went to a CEX store who offer £296 for a voucher for a G2 32gb simfree. They ran their own IMEI check and said they couldn't take my phone. It wasn't showing as stolen (I check IMEI numbers on https://www.imeidetective.com/ - worth doing whenever you're looking at buying a seccond hand phone- if you can). However, because I'd contacted Three to block my handset for a day, it was showing on CEX's system as having been blocked in the past, even though it wasn't showing as blocked now. CEX's policy is, apparently, not to buy phones that have been blocked - at any time. So, now I can't sell it at CEX- though I can sell it at other stores, which don't give as good a price as CEX- c'est la vie.