Need to fully separate two subnets sharing same internet link

Real quick guys, i have two subnets :A 10.0.0.0 and B 192.168.1.0 separated by a linksys router.Wan Port for the linksys is 10.0.0.220.
Subnet A is connected to a Netgear firewall/router behind the internet modem with routes to our other office sites(except subnet B) and to the internet.The linksys router is supposed to give subnet B access to the net, but unfortunately also gives access to subnet A resources.
I need for subnet B not to be able to access resources on subnet A.
I am thinking of directly linking the linksys with its own internet access and separate netgear firewall for internet. Any ideas guys?Need answers like yesterday.Thanks.