So, basically I just installed a Sonoff IP cam.
I called Maxis and got myself a public IP address.
TM modem -> TP-Link Archer C5v -> TP-Link Deco P7.

I setup port forwarding on both routers.

The  CCTV IP cam is viewable from my mobile phone on public network - No problem at all here.

My only concern here is how long will this last until the public IP address is renewed?

Are there any 100% free DDNS services out there which doesn't require you to confirm hostname every 30 days?

My Deco P7 is a new router, it has TP-Link DDNS service but the problem is it is connected to the Maxis C5v router.

I cannot get rid of the C5v as family members make use of the phone (connected to the C5v)  to make Voice calls. Will setting the C5v to bridge mode make the phone unusable?

Any suggestions appreciated.

I just discovered that TP-Link also has free DDNS. I tested it today and it appears to be working. Let's hope it's really free and no catches. So far so good.

Use apps, or use maxis official website there can login.

Really bro.

I'm using pfsense and kerio control as firewall on server. You may Google those 2 product and you'll understand. Those thing also can do as internet gateway.

Using Archer C5v, apparently by default the firewall on the router is toggled on and it blocked my devices from finding and connecting to my first gen Chromecast.

Disabling firewall, fixes the issue.