I guess you just need to follow what I wrote in my other post. Try contacting your provider to
see if they will give you a true IPv4 "routable" IP number. You may have to pay extra for it. If
not, you may be able to get out of your contract, because the service essentially does not work
as expected.
The subject of VPN is too complex to go into details here. I suggest that you Google and maybe
find information available in Greek. This technology has become somewhat cheaper, since I have
even seen a VPN based upon Raspberry Pi. The main problem is portability and getting it up in the
first place.
73,
Mitch DJ0QN / K7DX