If your e-ticket begins with 784, you should be able to access seat selection on the website. If it doesn't, give up now. If it does, check that you are using the correct name, with a / between surname and first name. I would probably not bother emailing. If you're in a city where they have a physical office, I'd go and see them. I've never heard of them charging for seat selection (but I haven't flown economy).