Port forwarding not working with Motorola MG7540 (modem/router)

Good evening,

On my Motorola MG7540 I set up port forwarding from 

my modem/router WAN IP address : port 3128 => my laptop LAN IP address : port 3128

[TCP]

I configured my laptop to have a static LAN IP address (for convenience)

I have a service running on this TCP port 3128

From my LAN (home network) this service is accessible by my laptop LAN IP address : port 3128

I want this service to be accessible from the outer Internet by my modem/router WAN IP address : port 3128

However, it doesn't work. For the test, I even turned off firewalls on this Motorola (modem/router) and on my laptop with no luck/change.

I suspicious that Xfinity tracks what ports are being forwarded and only open those ports on Xfinity firewall and all other ports are blocked. It looks like Xfinity has a firewall between the Internet and my modem/router and such the firewall is not synced with my modem/router.

If this is the case, maybe I need to get the port to be opened/synced manually on the Xfinity firewall?

Hmmm... maybe I need to renew WAN Lease (renew my public IP address?)? Not sure if it is gonna work though...

So any help or suggestion how to fix the issue?

P.S.

And from my home network the service available via both IP addresses: WAN and LAN ones. Which means that the forwarding per se works but it looks like if a request comes from the outer Internet such the request gets blocked.

P.P.S.

I rebooted both my laptop and the modem/router several times -- nothing changed.

P.P.P.S.

Maybe I need to change setting of my modem/router? I turned off "WAN Blocking" -- it did not change anything.

If it's more productive to discuss it with the Xfinity tech personnel, let's do it. I would share all the details. 

Regards,

[Edited: Personal Information]