Calling an existing column from SP in XSL code

I have a registration form in XSL and I want to include how many FreeSeats are available. 

I created a new Column in the List called FreeSeats and created a formula that takes TotalSeats - BookedSeats.

Now I want to call the FreeSeats in my XSL code. But I can't get the column to populate.

<xsl:call-template name="dvt.headerfield" ddwrt:atomic="1" xmlns:ddwrt="http://schemas.microsoft.com/WebParts/v2/DataView/runtime">

<xsl:with-param name="fieldname">@FreeSeats</xsl:with-param>

<xsl:with-param name="fieldtitle">FreeSeats</xsl:with-param>

<xsl:with-param name="displayname">FreeSeats</xsl:with-param>

<xsl:with-param name="sortable">1</xsl:with-param>

<xsl:with-param name="fieldtype">x:number</xsl:with-param>

</xsl:call-template>

I believe you can put code in to check what columns you have but I couldn't get that code to return anything. 

Any help would be appreciated.