When using Helm, and a user makes a payment via WorldPay, they are given the following message:
There is no way of getting back to Helm via the interface either.
This problem is caused by misconfiguration of the Worldpay Administration site.
In WorldPay, go to the Callback Installaton and then deselect the checkbox "Use Callback Response".
When a user pays they will then be sent to your resultY.html page defined in your WorldPay config. If they cancel the transaction whilst in WorldPay, they get presented with your WorldPay defined resultC.html page.