Incoming port blocking by ISP
Solution 1:
What they have done is that they have set up Carrier Grade NAT (CGN). Simply explained you are behind a big router shared with all the other subscribers.
If they were to open e.g. port 8000 for you, they would have to forward the port from the one external IP you all share to your IP, and this could not be done for others - for that reason there are no open ports.
If you get a static IP you would no longer be behind the CGN, and you could manage ports as you want to.