An update for you all.
After much arm twisting this issue has been resolved. They agreed to give me 2.5million credits in compensation, which were added instantly to my profile. As you all know, you can't buy tonnes of cars with that, but it all helps, and I'm buying a couple of cars a day now. I'm therefore satisfied the issue has now been dealt with.
@Gt_Sci now you mention it, I believe this may have happened to me - the black screen you mention with no loading progress may have caused this, but as you say, what else do you do in this scenario other than quit the game? Never mind...