I complete this entry to now, at long last, close my issue and by so doing put this issue to bed.
I received an instruction from Virgin Media to re-insert the new SIM and leave it installed. This I did, and left my mobile switched on and on charge, despite the only item on the screen showing was "Enter Subsidy Code" . This also meant that my mobile was out of service for me.
After a long delay, days not hours, I re-visited the "virginmedia.com/simhelp" website. Eventually I re-located the submission form to again register my complaint/problem. This form has a had a couple of new fields added and so a bit more relevant information was included (and some irrelevant information no longer required. I reiterated my problem and re-submitted the form.
After a further delay, I received an email from Virgin Media, issuing me with a new "Unlock code" and carrying the word "Code:" and an eight digit number.
I entered this "Unlock Code" or Code into my mobile as the Subsidy Password and my mobile then moved on to the next stage of asking me for my Unlocking Code. I entered the number so described on the card that had originally carried my new SIM and lo and behold my mobile "fired up" (still containing the new SIM). I quickly checked that it was working, and it was and is.
My account balance has now been transferred to the new SIM, albeit without the money that was "lost" phoning Virgin Media's Pay for help numbers.
I have still to re-format my mobile and add updated security passwords, etc.
So, my patience has been rewarded and I am now able to use my mobile with the new SIM.
Thank you to Virgin Media. I am pleased to be up and running again. But it is a real shame that my patience was strained to the limit and I have suffered many anxious days not knowing whether I was going to lose my mobile service, my money and my relationship with Virgin M.
June_of_Dorset