Just got an email from someone else (surprise, surprise) about the same subject so i thought id share the info:
Get in touch with Companies House, they will have the address for the person who set the company up (you will need the company number to do this)
Contact ofcom and explain the situation to them, they might be able to help you in tracing the person
If youve not got any paperwork then theres not much you can do am afraid, the other alternative is get in touch with the network and downgrade to the lowest tariff possible!
other than this theres not much else you can do!
hope it helps and let me know how you get on!
Shehzad Ilyas