I've got the China Visa for Double Entry, now i want it multiple, wht can i do?

I'm the Costa Rica Citizen , i will go to HK and China and Macau next month, and i 've apply the China Visa for Double Entry. But now i found that i need the multiple visa, double visa is $20000, can i add on $6000 to get the multiple visa? or i need to apply it again? Thx