Can't access certain sites

[#1]

Can anyone advise, can't seem to connect to my bank either via iphone app, Ipad app or laptop using my plusnet wifi, most other sites are fine have tried, various search engines.

Seem to get front page ie halifax.co.uk then it says server not found.  If I do it through internet explorer it says DNS problems.

Any ideas can;t get hold of technical support queing time over hour

[#2]

Try changing your DNS settings to (Google's)-

8.8.8.8

8.8.4.4

Do this on your router, though you can't if PN's Hub One.

Otherwise alter on individual devices