Was this for the tax year ended 5 April 2009? Do you complete a tax return or a repayment claim form (R40)?
I would two things
First, phone them up and get them to confirm that they have received your return and ask when you can expect the refund. If you gave them your bank details double check all is correct as if there is an error the repayment doesn’t arrive
Second, if you do fill in a return, register online at <a class="postlink" href="http://www.hmrc.gov.uk" onclick="window.open(this.href);return false;">http://www.hmrc.gov.uk</a> , as it is easier to complete your return (for next year) and the repayment follows quicker. You can also view online your account position and if the return has been processed you can see if they agree with how much they owe you.
If you do speak with someone take there name and ask if you can call them back if there has been no action after a few days.
Hope this helps