i have posted prices but price is lower when booking

i am really stuck. i can not understand why when someone books my property they pay less than what i have posted. i have only the standard rate and have not added any promotions. i have only added that if fewer people there is a discount but then booking gives them even another discount. Why is this happening and how can i stop it. I have looked and looked on the site and there is no phone number for me to call. 
thank you for any help