Ports needed to be opened for Remote access

I was trying to connect to a Remote AC500 PLC which is connected to a router with an Internet Static IP
I have opened all ports of the PLC for a trial basis but unfortunately, it wasn't a success. My router is not under NAT I have checked it using tracert command in Windows.

Ports are open while checking with port scanners but I am unable to access the PLC

What will be the issue?

I have tried forwarding a single port 1201 yet no difference

Kindly advise me on this

wr