Which line is it you're after?
As far as I can work out they operate two information lines:-
National Britannia LtdCaerphilly Business Park,
Caerphilly,
CF83 3GG
02920 266200 is listed as the Info line for Incident Reporting in the
Verified database. There are also some other entries in the
Unverified database as well.
I couldn't find any reference to 0870 on either site so it could be they've changed the numbers to 0845 but still keep the old ones in use for those that aren't aware they've changed numbers and in the mean time can earn money from the call.
Could you clarify which specific line you're after and check the numbers listed in both databases to see if they're of any help to you.