Okay, as threadstarter I should probably add my experience now ;-)

I wrote them (Novotel Heathrow) two emails, to which I never got an answer. Finally I decided to send them a friendly fax. A day later I got my invoice on the fax. I immediately send it to customer service via the web form and got my points credited within 2 hours.

Well, let's see if every 8th stay gives me that much trouble. I might just use different hotels.