If you have configured port forwarding and it is not working and your Fixed IP SIM provider have assured you that it is not their network blocking any ports and you think it is a problem with the router then you can perform a simple test.
connect your PC to the LAN of the router
download a simple web server (for example http://tinyserver.sourceforge.net/)
install and run the web server and confgure the web server port – for example if you think that the router is not port forwarding to port 8890 then give your web server the port of 8890
Then configure port forwarding – external port 8890 to forward to the IP address of your PC running the web server and internal port 8890
Then simply use a different PC connected to a different internet service and visit the public IP address of your router (assuming you are using a fixed IP SIM card with public IP address) and the port 8890 eg 188.8.131.52:8890
Your request will hit the router, the router will port forward to the PC running the web server and will use the internal port that you are testing and you will see the web page of the web server running on that PC
This will then confirm that your router port forwarding settings are working.
You can now investigate your other device on the LAN to determine why you are not able to connect to your device – the usual problem is that the device LAN settings are incorrectly configured.
You can test your open ports using an online tool such as http://mxtoolbox.com/PortScan.aspx