Sage Pay - Magento

Hi All, We want to use SagePay (Protx) as a payment option which we have setup with SagePay, put in all the details needed but when we go to purchase something in the test mode we get an error: “This transaction attempt has failed. Please use the Proceed button go back to the web store from which you were purchasing. The details of the failure are given below. Status: MALFORMED Status Detail: 3107 : The BillingSurname field is required.” When we then ring SagePay they say they now have a new protocol which puts all the billing information into one field when they receive it, so obviously leaves out the Billing Surname. Any ideas what could be the issue / any possible upgrades / extensions that would fix this? We are looking for someone who can fix this issue for us and get SagePay working correctly. Please let me know if this is something you have done before.