Simple Travel Insurance is the trading name of Acumus Insurance Solutions, which is part of The Primary Group, whose head office is in london (020 7743 0200). 

According to The Primary Group website, Acumus Insurance Services Limited have the same address as Simple Travel Insurance  http://www.primarygroup.co.uk/site/contactus.asp

I gave the London Head Office a call asking for the telephone number of Acumus in Altrincham.  She only had an 0870 number.   Interestingly, she said she had never heard of Simple Travel Insurance.

I explained that I was looking for an 01 number and she gave me the name and number of Acumus  Managing Director's Secretary (?), Lin Izzard on 0161 906 1717 and said that she may be able to help further.

Might be worth a call to her tomorrow to see if she can help you further.