FG100: WAN1 STATIC IP, WAN2 PPPOE (Have 1 static IP), Cannot access WAN2 from outside

Help!!!

I have DUAL WAN from 2 ISP.

WAN1 use static IP: (EX: IP: 1.2.3.4, Gateway: 2.3.4.5) i already config static route 0.0.0.0/0.0.0.0 DW: 2.3.4.5 (Distance = 5, priority = 0)

WAN2 use PPPOE (i have block 1 static IP) (EX: IP: 7.8.9.10, Gateway retrieved from ISP : 5.6.7.8 Distance = 5, priority = 10).

Firtstime i could access from outside to WAN1 and WAN2 normally.

But today it's not. 

i saw in WAN2 the Default gateway retrieved from server has been change to : 9.10.11.12.

How can i resolve?

PLS help!