While it is true that a small number of landline providers offer inclusive calls to 0870 numbers this is very much an anomaly in the market, with a very long history of how this happened. These numbers are actually premium rate numbers. Services operating on these numbers (with a Service Charge of more than 7p per minute) are defined as Controlled Premium Rate Services and are regulated by PSA.
It seems they have completely failed to comply with the Ofcom requirements in force since 1 July 2015:
https://www.ofcom.org.uk/phones-telecoms-and-internet/advice-for-consumers/advic...Likewise, they have failed to comply with the BIS requirements in force since 13 June 2014:
http://www.legislation.gov.uk/uksi/2013/3134/regulation/41/madeBreaches of the Ofcom requirements should be reported to ASA.
Breaches of the BIS requirements should be reported to Trading Standards via the Citizens Advice national Consumer Helpline either on 0345 404 0506 or via the report form on their website.