As someone who (presumably) knows a bit about computers, we need to put information in to get information out. 

From Whois of portland.co.uk the address is:
5 Portland Avenue
New Malden
Kent
KT3 6AX

A search of 192.com gives one result for Portland Communications Ltd: 0870 199 5108
The address given on 192.com is a PO Box:
PO BOX 357
New Malden
Surrey
KT3 6WN

A check of the Internet Archive shows that they've been using various 0870 numbers since about 2000.

However, clicking on any of the 1999 archives gives 0181 942 1115. A check of my Code Cracker shows 0181 942 to be New Malden. Of course, this is now 020 89421115. The number is still in service and appears to divert to a mobile, as it goes to answerphone.

A search of "020 8942 1115" throws up a couple of results.

I suggest that you try numbers around that one.

A Google shows 020 8942 1100 is Alpha Business.

BTW Did those Freeola numbers work?