parabellum,
It looks more and more like your ISP is making a dog's breakfast of this.
I'm assuming that you have your PC directly connected to their ADSL modem.
You have your PC set to obtain IP and associated settings via DHCP - i.e. automatically. So the only place you can get them is from the ISP. If they are wrong it is totally down to your ISP to fix it.
All Ahead Full has posted a working DNS server 212.227.39.54 - I have tested with it and I can use it, so please can you enter that into your IP settings:
select "Use the following DNS Server Addresses",
* enter 212.227.39.54 as the Preferred DNS Server.
See what happens.
SD