Hello IAVOID0870 and welcome to the forum. Thank you for posting the information on this company. They regard themselves as "approachable" on the
contact page.
A check of
192.com reveals only the 0870 numbers.
Looking back at their website on
Internet Archive shows that they adopted 0870 numbers in 2002. The earliest link takes us back to 25 May 2002, and the homepage shows 0870s. Strangely, by clicking on links on that page, it goes back to February 2002 with the 0151 number mentioned by Crabtree. It also has a fax of 0151 666 1825 and "RTA Fax" of 0151 647 0124.
IAVOID0870, how do you know that they have numbers starting 0151 637xxxx?
Do they have many 0870 numbers, ie one for each person? If so, they may map straight to geographicals. Eg 0870 1234xxx -> 0151 9876xxx