Previously, I noted that I was finding it difficult to cancel my booking. The phone lines were difficult, as nobody picked up for up to an hour at a time. But I sent an email and just received confirmation that my booking has been canceled. So, my advice is to cancel via email and not waste your time trying to contact them over the phone. (Really, they should have an online option... but whatever.)
Prompt email reply, though. So, that was nice.