What I find about the UK Conde Nast subscription service is that everyone you speak to is helpful - but they seem to have a computer system that simply isn't up to the job. Over the years, there are times I've called them to make a simple change of address, and it's taken several phone calls over two months in order to get things straightened out, because the computer has reverted to using an old address. So I don't have much faith in them being the most effective of customer service departments.
As for late subscription issues, I wouldn't mind if they were late every now and again, but I get mine late most months - in fact, I think there was one month last year when the subscription copies were delayed for several weeks, due to a "warehouse problem". Meanwhile, the issue is sitting in the shops and you're itching to get it - but why pay twice over for a magazine when it wasn't your fault it didn't arrive on time? Shoddy.