Seeing as this thread seems to have life after my problem has been solved, I thought it might help to add a bit more detail...
My 1st 'chat' conversation didn't seem to have achieved much, but the person I spoke to must have found my account and added some notes - even though he couldn't do much more and advised me to phone.
I think my first phone call was a complete waste of time...
But, when I then tried chat a few days later, they quickly spotted the notes, realsised they couldn't help, but knew I needed to be put through to 'The Department That Deals With That'!
He then offered to call me on my current (non-Vodafone) mobile so he could then put me through to the correct Department. Sure enough, a couple of mins later, my phone rang, a quick verification that I was who I said I was (ie security questions - obviously V still have my data!) and he put me on hold for a couple of minutes.
The next person I spoke to was from 'The Department That Deals With That'. He was immediately aware of tmy account and the Sure Signal. Checked that it was the one I wanted deregistering. Advised me that because it hadn't been used for so long it was INACTIVE, but that is not the same as DEREGISTERED. So, he ACTIVATED it (took about 10 seconds), then DEREGISTERED it (another 10 seconds). Done!!
He advised that it must be left for 24 hours (probably very much on the safe side), but can then be REREGISTERED by a new user. Phew!
.png "Moderator (Retired)"){kind=icon}
