WooCommerce / WorldPay callback redirecting issue

I'm having an issue with WooCommerce and WorldPay. It was all working fine on my old server but we recently changed servers and now orders are going through but they're not coming back to WooCommerce. We get an email so can process the orders but it's a bit of a pain.

According to WorldPay...

"It looks as your server where your website is sitting on is trying to redirect the call back as soon as WorldPay gets to your website. You will need to go back to the developer and get a meta data refresh tag added to the callback page of about 3 seconds."

The thing is I've no idea a) why this has started happening or b) how to make the fix they're suggesting.

Anyone got any ideas?