Bizarre issue when upgrading to new o2 phone

[sickscenes]

I recently upgraded my old phone to a new one via o2. 

New phone was sent out quickly, I used samsung smart switch to facilitate transferring of data to my new phone. 

Data transferred, old phone immediately stopped working and new one sprang to life. Great, I thought, that was super simple. 

After a few weeks I thought I should try to sell my phone to a retailer as I couldn't invisage ever using it again. When I tried to do this, they said the IMEI had been blacklisted as lost or stolen! 

I've never reported the phone lost or stolen so perplexedly contacted o2 customer service on 202 - none of them could see an IMEI block at their end despite repeated calls.

Eventually I went into the local o2 store who were very helpful and actually found the blacklist IMEI and have raised a ticket. 

Thing is, I have NO idea why the IMEI is blacklisted. My old phone worked absolutely fine up until the minute of the switch, and my account payments etc are all up to date. 

Has anyone had an experience like this or could shed some light on it? Would love some info on what it could be.  

[pgn]

Someone on O2 side misclicked a button or a checkbox perhaps, @sickscenes? They are incentivised to sell contracts on the O2 side, so I suspect a (painful, in your case) manual error, @sickscenes - and you've got a ticket open now with O2, rightly, to resolve and remove your old phone's IMEI from the blacklist - good.