Hi Darren
If you see order from back-end after you completed payment at Worldpay but don't receive notification email, then it might be a setting with your mail server. Could you try to create a new Joomla users from back-end to see whether the email is sent to him or not ?
For Worldpay, to be honest, I don't have much experience with it. However, it seems for a Worldpay account, you can have different installations and each installation can have a different Response URL ? Could you please try to contact worldpay support about it ?
If not, we will have to edit code of the plugins to make it works with the two extensions.
Tuan