Modem/Router -> Router -> DVR

Hi everyone, I've been scouring all over the web to find answers for this problem but couldn't find anything that can help me. I was wondering if anyone can help me out:

I used to have a PPPOE modem that was working fine with my DVR (with ddns via dyndns), but recently our ISP has upgraded and changed our modems to DHCP. The problem is that it doesn't allow me to go bridge mode so my router gets a local IP address.

I have this setup: Modem/Router -> Router -> DVR

1. Modem/Router (DHCP, but cannot do bridge mode) ZTE ZXV10 W300S Local IP: 192.168.1.1 Subnet: 255.255.248.0

2. Router (bridge mode) Linksys E2500 Local IP: 192.168.1.2 Subnet: 255.255.255.0 (I've also tried changing to 255.255.248.0)

3. DVR H.264 Network DVR Local IP: 192.168.1.10 Subnet: 255.255.255.0 (I've also tried changing to 255.255.248.0)

I did port forward 80 (but seems like ISP is using it so it's blocked) and I also did port forward to 9000 (I checked the port is open). Accessing it from my local host is working, but when I try with my external IP, I couldn't connect to it.

Can anyone help me out? Thank you in advance!