I go twice a week just because it keeps me thinking about things. I also weigh daily in the morning, so those numbers are much more consistent because I don't deal with the time of day/food/clothing issues.

Do what you need to do-- you are paying them, not the other way around. If you were cheating because you only went once a week, then I can see their point, but if things are fine for you, then do what works best. Just be sure you're being honest with yourself. Sometimes that's the hardest part. :)