This morning - no reply to the e-mail; ticket still open, under “unsolved”.
Just now - still no reply to e-mail; ticket has been closed and moved to solved, although there has been no reply to it.
Next step is to write to their registered address, following the guidelines on the ICO site. I’ll be surprised if that produces results. Although their website claims that they’re running the business from the registered address in London, I have reason to believe most - if not all - the staff are based several thousand miles away. Anyway, if that doesn’t sort things out, then I can refer it to the ICO.
(Total cost - 63p for a stamp. )