Discovery only cover a 1/3 what they should cover

Extremely frustrated by Discovery Health and their poor coverage for dental work. Apparently, almost no dentists charge anywhere close to their Discovery rates. Despite being on the list of covered dentists on their website, and supposedly only requiring a R150-copayment for the list of procedures given by discovery (consultation, cleaning etc.), Discovery are only paying out a 1/3 of the dentists charge - including the R150 copayment. I didn't even need the dentist, but thought I should go for the yearly check-up that they recommend. Is it that hard to create a consolidated list of the dentists that they actually cover? Poor service