When you first joined the company, like most you are given a 14 day cooling off period that allows you to change yer mind and get a full refund, with renewal, I'm not so sure if the same applies, give em a ring!
Worst case scenario, you canx the policy and you would be charged to Time on Risk, i.e just charged for the X number of days you spent on cover. Pro rata refund woud apply
However ask about cancellation charges before you do anything. Also enquire if they charge "Short Term Rates" STR's are a thing of the past, but some companies still do employ STR's . i.e Canx a policy after 2 weeks, you are charged for 1 months cover.
You will need to canx the policy in writing, usually requires you do post in written request and return f the policy schedule, most companies will accept a fax thou.